Modified vaccinia ankara virus variant and cultivation method

ABSTRACT

The present invention provides an attenuated virus, which is derived from Modified Vaccinia Ankara virus and characterized by the loss of its capability to reproductively replicate in human cell lines. It further describes recombinant viruses derived from this virus and the use of the virus, or its recombinants, as a medicament or vaccine. A method is provided for inducing an immune response in individuals who may be immune-compromised, receiving antiviral therapy, or have a pre-existing immunity to the vaccine virus. In addition, a method is provided for the administration of a therapeutically effective amount of the virus, or its recombinants, in a vaccinia virus prime/vaccinia virus boost innoculation regimen. The present invention relates to a method of virus amplification in primary cells which are cultivated in a serum free medium. Viruses produced by this method are advantageously free of any infectious agents comprised in animal sera.

FIELD OF THE INVENTION

The present invention provides an attenuated virus which is derived fromModified Vaccinia Ankara virus and which is characterized by the loss ofits capability to reproductively replicate in human cell lines. Itfurther describes recombinant viruses derived from this virus and theuse of the virus or its recombinants as a medicament or vaccine.Additionally, a method is provided for inducing an immune response evenin immune-compromised patients, patients with pre-existing immunity tothe vaccine virus, or patients undergoing antiviral therapy. The presentinvention also provides a method for the cultivation of primary cells.The primary cells are cultivated in a serum free medium comprising afactor selected from the group consisting of growth factors andattachment factors. The method for the cultivation of primary cells maybe one step in a method for the amplification of viruses, wherein thecells are then infected with a subject virus and the infected cells arecultivated in serum free medium until progeny virus is produced. Theinvention encompasses the cultivation of poxviruses according to thismethod.

BACKGROUND OF THE INVENTION

Modified Vaccinia Ankara (MVA) virus is related to vaccinia virus, amember of the genera Orthopoxvirus in the family of Poxviridae. MVA wasgenerated by 516 serial passages on chicken embryo fibroblasts of theAnkara strain of vaccinia virus (CVA) (for review see Mayr, A., et al.Infection 3, 6-14 [1975]). As a consequence of these long-term passages,about 31 kilobases of the genomic sequence were deleted from the virusand, therefore, the resulting MVA virus was described as being highlyhost cell restricted to avian cells (Meyer, H. et al., J. Gen. Virol.72, 1031-1038 [1991]). It was shown in a variety of animal models thatthe resulting MVA was significantly avirulent (Mayr, A. & Danner, K.[1978] Dev. Biol. Stand. 41: 225-34). Additionally, this MVA strain hasbeen tested in clinical trials as a vaccine to immunize against thehuman smallpox disease (Mayr et al., Zbl. Bakt. Hyg. I, Abt. Org. B 167,375-390 [1987], Stickl et al., Dtsch. med. Wschr. 99, 2386-2392 [1974]).These studies involved over 120,000 humans, including high-riskpatients, and proved that compared to vaccinia based vaccines, MVA haddiminished virulence or infectiousness while it induced a good specificimmune response.

In the following decades, MVA was engineered for use as a viral vectorfor recombinant gene expression or as a recombinant vaccine (Sutter, G.et al. [1994], Vaccine 12: 1032-40).

In this respect, it is significant that even though Mayr et al.demonstrated during the 1970s that MVA is highly attenuated andavirulent in humans and mammals, some recently reported observations(Blanchard et al., 1998, J Gen Virol 79, 1159-1167; Carroll & Moss,1997, Virology 238, 198-211; Altenberger, U.S. Pat. No. 5,185,146;Ambrosini et al., 1999, J Neurosci Res 55(5), 569) have shown that MVAis not fully attenuated in mammalian and human cell lines since residualreplication might occur in these cells. It is assumed that the resultsreported in these publications have been obtained with various knownstrains of MVA since the viruses used essentially differ in theirproperties, particularly in their growth behavior in various cell lines.

Growth behavior is recognized as an indicator for virus attenuation.Generally, a virus strain is regarded as attenuated if it has lost itscapacity or only has reduced capacity to reproductively replicate inhost cells. The above-mentioned observation, that MVA is not completelyreplication incompetent in human and mammalian cells, brings intoquestion the absolute safety of known MVA as a human vaccine or a vectorfor recombinant vaccines.

Particularly for a vaccine, as well as for a recombinant vaccine, thebalance between the efficacy and the safety of the vaccine vector virusis extremely important.

Most viral vaccines such as attenuated or recombinant viruses aremanufactured from cell culture systems. The cells used for virus/vaccineproduction may be cell lines, i.e. cells that grow continuously invitro, either as single-cell suspension culture in bioreactors or as amonolayer on a cell-support surface of tissue culture flasks orroller-bottles. Some examples for cell lines used for the production ofviruses are: the human fetal lung cell-line MRC-5 used for themanufacture of polio viruses and the human fetal lung cell-line WI-38used for the manufacture of measles virus, mumps virus and rubella virus(MMR II) (Merck Sharp & Dohme).

Not only cell lines but also primary animal cells are used for themanufacture of vaccines. An example of primary cells that are used forvirus production are chicken embryo fibroblasts (CEF cells). These cellsare used for the production of measles and Japanese encephalitis virus(Pasteur Merieux), mumps virus (manufactured by Provaccine), rabiesvirus (manufactured by Chiron Berhing GmbH & Co.), yellow fever virus(manufacture by Aprilvax), influenza virus (manufactured by Wyeth Labsand SmithKline & Beecham) and modified Vaccinia virus Ankara (MVA).

CEF cells are often used since many virus vaccines are made byattenuating the virulent disease-causing virus by serially passaging inCEF cells. Attenuated viruses, such as MVA are preferably not propagatedon human cells since there is a concern that the viruses might becomereplication competent in cells of human origin. Viruses that haveregained the ability to replicate in human cells represent a health riskif administered to humans, in particular if the individuals are immunecompromised. For this reason, some attenuated viruses, such as MVA, arestrictly manufactured from CEF cells, if intended for human use.

Moreover, CEF cells are used for those viruses that grow only on saidcells. Examples of such viruses are avian viruses such as avipoxviruses, canary pox virus, ALVAC, Fowl pox virus and NYVAC.

Cell lines and primary cells grown under in vitro culturing conditionsrequire a special growth and maintenance medium that can support (I)cell replication in the logarithmic phase and (II) cell maintenance oncethe cells are no longer dividing, i.e., when the cells are in thestationary phase. The commonly used cell culture media comprise a richsalt solution containing vitamins, amino acids, essential trace elementsand sugars. Growth hormones, enzymes and biologically active proteinsrequired for supporting cell growth and maintenance are usually added asa supplement to the medium in the form of an animal blood derived serumproduct. Examples of animal blood derived serum products are fetal calfserum, chicken serum, horse serum and porcine serum. These sera arederived from fractionated blood, from which the red blood cells and thewhite blood cells have been removed. Primary cells, such as CEF cellsare even more dependant on animal serum sources than cell lines. Thus,primary cells are usually cultivated in cell culture media comprising 5to 10% serum, in most cases fetal calf serum (FCS).

The animal sera not only comprise factors that are required for thegrowth of cells, but also factors that are required for cells thatnaturally grow as adherent cells to attach to the cell support surfaceof the culture vessel. Thus, it is critical for adherent cells thatenough serum is added to the medium to enable them to grow and form amonolayer.

Unfortunately, bovine/fetal calf serum as well as sera from otheranimals may contain adventitious pathogenic agents such as viruses orprion proteins. There is a potential risk that these pathogenic agentsmay be transmitted to the animal/human to be treated or vaccinated withthe vaccine or any other pharmaceutical product produced in cellculture. This is of particular relevance if cell culture products areadministered to immune-compromised humans. One of the many potentialmajor problems associated with the commonly used bovine serum supplementis the possibility to transmit the agent causing bovine spongiformeencephalopathy (BSE) to the animals/humans that come into contact withthe products produced from cell culture.

In view of the possible risk associated with the use of animal sera incell culture it has become clear that manufacturing processes free fromthe use of animal products are highly desirable.

To this end, specific media that do not have to be supplemented withanimal sera have been developed for continuously growing cell lines andfor the production of viruses in continuously growing cell lines,respectively. An example of such a serum free medium that can be used tocultivate cell lines is VP-SFM manufactured by Gibco BRL/LifeTechnologies. According to the manufacturer's information VP-SFM isdesigned specifically for the growth of VERO, COS-7, MDCK, Hep2, BHK-21and other important cell lines (Price, P. and Evege, E. Focus 1997, 19:67-69) and for virus production in said cell lines. No information isavailable regarding the cultivation of primary cells in the medium.

THE PRESENT INVENTION SUMMARY OF THE INVENTION

What we therefore believe to be comprised by our invention may besummarized inter alia in the following words:

A method for the amplification of a virus comprising:

-   -   cultivating primary avian cells permissive for productive        replication of the virus in a serum free medium comprising a        factor selected from the group consisting of growth factors and        attachment factors,    -   infecting of the primary avian cells with the virus,    -   cultivating the infected cells in serum free medium until        progeny virus is produced, and    -   isolating the virus from the culture; such a

method wherein the serum free medium comprising growth factors andattachment factors is removed at the time of infecting the primary aviancells with the virus, and/or during cultivating of the infected cellsuntil virus progeny is produced, and replaced with a serum free mediumwhich does not comprise growth factors and attachment factors; such a

method wherein, subsequent to cultivating the infected cells in serumfree medium until progeny virus is produced, one or more viruspurification steps are performed; such a

method wherein the virus used for infection of primary avian cells waspreviously propagated or may have been previously propagated in thepresence of animal sera and is subsequently re-derived through severalrounds of plaque purification by limited dilution in serum free mediumto reduce the risk of serum contamination; such a

method which is repeated at least once to obtain a virus or virus stockwhich is essentially free of products and/or infectious agents comprisedin animal sera; such a

method wherein the primary avian cells are Chicken Embryo Fibroblasts(CEF); such a

method wherein the growth factor is an epidermal growth factor (EGF);such a

method wherein the epidermal growth factor (EGF), is recombinant-humanEGF; such a

method wherein the concentration of EGF is in a range of 5 to 20 ng/mlmedium; such a

method wherein the attachment factor is fibronectin; such a

method wherein the concentration of fibronectin is in the range of 1 to10 ug/cm² surface of the cell culture vessel; such a

method wherein the medium comprises two or more factors selected fromgrowth factors and attachment factors; such a

method wherein the medium comprises EGF and fibronectin in concentrationranges of 5 to 20 ng/ml and 1 to 10 ug/ml medium, respectively; such a

method wherein the medium further comprises one or more additivesselected from a microbial extract, a plant extract and an extract from anon-mammalian animal; such a

method wherein the microbial extract is a yeast extract or a yeastolateultrafiltrate; such a

method wherein the plant extract is a rice extract or a soya extract;such a

method wherein the extract from a non-mammalian animal is a fishextract; such a

method wherein the virus is selected from mumps virus, measles virus,rabies virus, Japanese encephalitis virus, yellow fever virus, influenzavirus and poxvirus; such a

method wherein the poxvirus is an attenuated virus or a recombinantvirus; such a

method wherein the poxvirus is an orthopoxvirus; such a

method wherein the orthopoxvirus is a Vaccinia virus; such a

method wherein the Vaccinia virus is Modified Vaccinia virus Ankara;such a

method wherein the Modified Vaccinia virus Ankara is selected fromMVA-575 deposited at the European Collection of Animal Cell Cultures(ECACC) under the deposition number V00120707, MVA-572 deposited atECACC under the deposition number V94012707, and MVA-BN deposited atECACC under number V00083008, or a derivative of any such virus; such a

method wherein the Vaccinia virus is an MVA-derived vaccinia viruscharacterized by replicating in vitro in chicken embryo fibroblasts andby being non-replicative in vitro in human cells which permitreplication of MVA vaccinia strain 575 (ECACC V00120707) and/or MVAvaccinia strain 572 (ECACC V94012707); such a

method wherein the MVA-derived vaccinia virus is further characterizedas being non-replicative in an immunocompromised mouse; such a

method of wherein the mouse is an AGR129 transgenic mouse; such a

poxvirus obtained by:

-   -   cultivating primary avian cells permissive for productive        replication of the virus in a serum free medium comprising a        factor selected from the group consisting of growth factors and        attachment factors,    -   infecting the primary avian cells with the virus,    -   cultivating the infected cells in serum free medium until        progeny virus is produced, and    -   isolating the virus from the culture; such a

poxvirus wherein the primary avian cells are Chicken Embryo Fibroblasts(CEF); such a

poxvirus wherein the virus used for infection of primary avian cells waspreviously propagated or may have been previously propagated in thepresence of animal sera and which virus is subsequently re-derivedthrough several rounds of plaque purification by limited dilution inserum free medium; such a

poxvirus wherein 4-6 rounds of plaque purification are performed; such a

poxvirus wherein the risk of the poxvirus to contain a BSE particle isless than 10³²; such a

poxvirus which is essentially free of any products and/or infectiousagents comprised in animal sera; such a

poxvirus wherein the poxvirus is Modified Vaccinia virus Ankara; such a

poxvirus wherein the Modified Vaccinia virus Ankara is selected fromMVA-575 (ECACC V00120707), MVA-572 (ECACC V94012707), and MVA-BN (ECACCV00083008), or a derivative of such virus; such a

poxvirus wherein the poxvirus is an MVA-derived vaccinia viruscharacterized by replicating in vitro in chicken embryo fibroblasts andby being non-replicative in vitro in human cells which permitreplication of MVA vaccinia strain 575 (ECACC V00120707) and/or MVAvaccinia strain 572 (ECACC V94012707); such a

poxvirus wherein the MVA-derived vaccinia virus is further characterizedas being non-replicative in an immunocompromised mouse; such a

poxvirus wherein the mouse is an AGR129 transgenic mouse; such a

poxvirus wherein the poxvirus is Modified Vaccinia virus Ankara; such a

poxvirus wherein the Modified Vaccinia virus Ankara is selected fromMVA-575 (ECACC V00120707), MVA-572 (ECACC V94012707), and MVA-BN (ECACCV00083008), or a derivative of such virus; such a

poxvirus wherein the poxvirus is an attenuated virus or a recombinantvirus; such a

vaccine comprising the poxvirus; such a

pharmaceutical composition comprising the poxvirus and apharmaceutically acceptable carrier, diluent and/or additive; such a

pharmaceutical composition which is essentially free of any productsand/or infectious agents comprised in animal sera; such a

method for enhancing a specific immune response to a vaccine in a livingmammal, including a human, comprising administering a vaccine and anadjuvant-effective amount of the poxvirus; such a

method for affecting a specific immune response in a living mammal,including a human, comprising administering an effective amount of apoxvirus; such a

method wherein the specific immune response is against an orthopoxvirus; such a

method wherein the specific immune response is against smallpox; such a

method for affecting an immune response against an HIV in a livingmammal, including a human, comprising administering an effective amountof a poxvirus; such a

method for affecting an immune response in a living mammal, including ahuman, comprising administering an effective amount of a poxvirus; sucha

method wherein the poxvirus is administered to a cancer patient; such a

method wherein the mammal, including a human, is immune compromised;such a

method wherein the poxvirus is administered as a vaccine; such a

method for inducing a specific immune response in a living mammal,including a human, comprising administering an effective amount of apoxvirus; such a

method wherein the specific immune response is against an orthopoxvirus; such a

method wherein the specific immune response is against smallpox; such a

method wherein the mammal, including a human, is immune compromised;such a

method wherein the poxvirus is administered as a vaccine; such a

method for inducing an immune response against an HIV in a livingmammal, including a human, comprising administering an effective amountof a poxvirus; such a

method for inducing an immune response in a living mammal, including ahuman, comprising administering an effective amount of a poxvirus; sucha

method wherein the poxvirus is administered to a cancer patient; such a

kit for prime/boost immunization comprising the pharmaceuticalcomposition for a first inoculation (“priming inoculation”) in a firstvial/container and for a second inoculation (“boosting inoculation”) ina second vial/container; such a

MVA-derived vaccinia virus characterized by replicating in vitro in CEFcells and being non-replicative in vitro in human cells which permitreplication of MVA vaccinia virus strain 572 (ECACC V94012707); such a

MVA-derived vaccinia virus which is non-replicative in animmunocompromised mouse; such a

MVA-derived vaccinia virus, wherein the mouse is an AGR129 transgenicmouse.

DETAILED DESCRIPTION OF THE INVENTION

According to a preferred embodiment of the present invention, newvaccinia viruses are provided which are capable of reproductivereplication in non-human cells and cell lines, especially in chickenembryo fibroblasts (CEF), but not capable of reproductive replication ina human cell line known to permit replication with known vacciniastrains.

Known vaccinia strains reproductively replicate in at least some humancell lines, in particular the human keratinocyte cell line HaCaT(Boukamp et al. 1988, J Cell Biol 106(3): 761-71). Replication in theHaCaT cell line is predictive for replication in vivo, in particular forin vivo replication in humans. It is demonstrated in the example sectionthat all known vaccinia strains tested that show a residual reproductivereplication in HaCaT also replicate in vivo. Thus, the invention relatesto vaccinia viruses that do not reproductively replicate in the humancell line HaCaT.

Adventageously, the invention concerns vaccinia virus strains that arenot capable of reproductive replication in any of the following humancell lines: human cervix adenocarcinoma cell line HeLa (ATCC No. CCL-2),human embryo kidney cell line 293 (ECACC No. 85120602), human boneosteosarcoma cell line 143B (ECACC No. 91112502) and the HaCaT cellline.

The growth behaviour or amplification/replication of a virus is normallyexpressed by the ratio of virus produced from an infected cell (Output)to the amount originally used to infect the cell in the first place(Input) (“amplification ratio). A ratio of “1” between Output and Inputdefines an amplification status wherein the amount of virus producedfrom the infected cells is the same as the amount initially used toinfect the cells. This ratio is understood to mean that the infectedcells are permissive for virus infection and virus reproduction.

An amplification ratio of less than 1, i.e., a decrease of theamplification below input level, indicates a lack of reproductivereplication and thus, attenuation of the virus. Therefore, it was ofparticular interest to identify and isolate a strain that exhibits anamplification ratio of less than 1 in several human cell lines, inparticular all of the human cell lines 143B, HeLa, 293, and HaCaT.

Thus, the term “not capable of reproductive replication” means that thevirus of the present invention exhibits an amplification ratio of lessthan 1 in human cell lines, such as 293 (ECACC No. 85120602), 143B(ECACC No. 91112502), HeLa (ATCC No. CCL-2) and HaCaT (Boukamp et al.1988, J Cell Biol 106(3): 761-71) under the conditions outlined inExample 10 of the present specification. Preferably, the amplificationratio of the virus of the invention is 0.8 or less in each of the abovehuman cell lines, i.e., HeLa, HaCaT, and 143B.

Viruses of the invention are demonstrated not to reproductivelyreplicate in cell lines 143B, HeLa and HaCaT. The particular strain ofthe invention that has been used in the examples is a derivative of avirus deposited on Aug. 30, 2000 at the European Collection of CellCultures (ECACC) under number V00083008. This strain is referred to as“MVA-BN” throughout the Specification. It has already been noted thatknown MVA strains show residual replication in at least one of the humancell lines tested. All known vaccinia strains show at least somereplication in the cell line HaCaT, whereas the MVA strains of theinvention, in particular MVA-BN, do not reproductively replicate inHaCaT cells.

Moreover, the invention concerns derivatives of the virus as depositedunder ECACC V0083008. “Derivatives” of the viruses as deposited underECACC V00083008 refer to viruses exhibiting essentially the samereplication characteristics as the deposited strain but exhibitingdifferences in one or more parts of its genome and/or cultured indifferent media including serum containing and/or serum free media.Viruses having the same “replication characteristics” as the depositedvirus are viruses that replicate with similar amplification ratios asthe deposited strain in CEF cells and the cell lines HeLa, HaCaT and143B; and that show a similar replication in vivo, as determined in theAGR129 transgenic mouse model (see below).

Adventageously, the virus of the instant invention is furthercharacterized in that it is cultured under stringent conditions. Thepresent invention provides a method for cultivation of primary cells, inparticular primary avian cells, in serum free medium and a method forthe production of virus in primary cells under serum free conditions.The instant method for the cultivation of primary cells may becharacterized in that the cells are cultivated in a serum free mediumcomprising a factor selected from the group consisting of growth factorsand attachment factors.

According to the present invention primary cells that naturally grow asadherent cells attach to the surface of the cell culture vessel afterseeding and grow in a logarithmic phase until a monolayer is formed.According to the present invention the resting cells may be maintainedin the medium used during the attachment and logarithmic growth of thecells.

The term “primary cells” as used in the present description is wellknown to a person skilled in the art. Without being restricted to thefollowing definition the term “primary cells” may refer to cells thathave been freshly isolated from an animal or human tissue, organ ororganism, wherein the cells are not able to continuously andindefinitely replicate and divide. Usually, primary cells divide in cellculture less than 100 times, often less than 50 times, often less than25 times. Thus, primary cells have not undergone an immortalizing event.Examples for primary cells are cord blood lymphocytes and human oranimal fibroblasts. Respresentative examples of animal fibroblasts areavian fibroblasts, such as Chicken Embryo Fibroblasts (CEF cells). Anexample of primary human fibroblasts is human foreskin fibroblasts.

Methods of isolating primary cells are known. Generally, primary cellcultures are derived directly from tissues, organs or embryos. Thetissues, organs or embryos are subjected to protease treatment to obtainsingle cells. The cells are then cultivated according to the method ofthe present invention under in vitro culture conditions.

More specifically, CEF cells are obtained from protease digested chickenembryos. CEF cells grow best as adherent cells attached to a solid cellsupport surface. The cells start replication and establish a monolayer.If CEF cells (after embryo digestion) are cultivated in vitro with astandard culturing medium and without animal serum, the cells willoccasionally attach to the solid cell-support surface, but will notreplicate to form a confluent monolayer of cells and will, with time,slowly detach from the solid culturing-support surface. In contrast, ifthe CEF cells are cultivated according to the method of the presentinvention, the cells attach to the solid support, grow in thelogarithmic phase until a monolayer is formed and can be maintained inthe stationary phase for several days.

The method of the present invention is not restricted to cells that formmonolayers. According to an alternative embodiment the method accordingto the present invention may be used for all other types of primarycells, such as cells naturally growing in suspension culture (e.g.lymphocytes or other types of blood cells) or cells that naturally wouldgrow as adherent cells but have been adapted to growing in suspensionculture.

As shown below the cells can also be used for the serum freeamplification of viruses that might be useful as vaccines.

Viruses, including e.g. wild-type viruses, attenuated viruses andrecombinant viruses that are used as vaccines, may be amplified underserum containing conditions. However as noted above, there is apotential risk that serum contains pathogenic agents (such as TSE/BSE)may be transmitted to the animal/human treated or vaccinated with thevaccine. To reduce the risk of contaminants in the vaccine, it is afurther aspect of the invention to passage and/or cultivate and/orplaque purify and/or purify by limited dilution or any other methodunder serum free conditions those viruses that previously have beenamplified under serum containing conditions and that have been used orare intended to be used as vaccine. A virus that may by used in avaccine and that is passaged and/or cultivated and/or plaque purifiedand/or purified by limited dilution or any other method under serum freeconditions may be a wild-type virus, an attenuated virus or arecombinant virus.

It was unexpected that primary cells naturally growing as adherent cells(I) can effectively attach to the surface of the cell culture vesselwithout forming unacceptable amounts of aggregates and (II) can be grownin the logarithmic phase in the absence of serum since it is generallybelieved that primary cells are dependant on a multitude of differentfactors and components comprised in serum. Moreover, it is believed thatadherent cells form non-viable aggregates that do not attach to thesurface of the cell culture vessel, when cultivated in serum freemedium. Thus, it was unexpected that it is sufficient to add to a serumfree medium a factor selected from the group consisting of growthfactors and attachment factors in order to obtain attachment and growthof adherent primary cells. Moreover, it was also unexpected that primarycells cultivated in suspension culture can be grown with the media usedin the method according to the present invention.

Furthermore, it was surprising that primary avian cells, such as theinstant Chicken Embryo Fibroblasts (CEF), can be cultivated to attach tothe surface of a cell culture vessel without forming unacceptableamounts of aggregates in a serum free medium comprising a factorselected from the group consisting of growth factors and attachmentfactors. Avian cells are otherwise understood to grow adversely in serumfree medium not comprising growth factors or attachment factors, i.e.,it was unexpected that the poor growth properties of primary avian cellscould be improved significantly by adding a factor selected from growthfactors and attachment factors to serum free medium.

The term “cultivation of cells” in a serum free medium in the context ofadherent primary cells refers to the seeding of the cells into theculture vessel in a serum free medium, to the growing of the cells in aserum free medium in the logarithmic phase until a monolayer is formedand/or to the maintenance of the cells in serum free medium as soon asthe monolayer is formed. The term “cultivation of cells” in a serum freemedium also refers to a method in which all of the above mentioned stepsare performed with serum free medium, so that no animal serum productsare present during the whole cultivation process of the cells. Thus, ina more general meaning the term “cultivation of cells in a serum freemedium” refers to the fact that all media leading to the formation of amonolayer are serum free media. The media used in all of the above stepsmay comprise a factor selected from growth factors and attachmentfactors. However, it might be sufficient to add such a factor only tothe media used for the attachment of the cells and/or the growing of thecells under logarithmic conditions.

The term “cultivation of cells” in a serum free medium in the context ofcells growing in suspension culture refers to the seeding of the cellsinto the culture vessel in a serum free medium, the growing of the cellsin a serum free medium in the logarithmic phase and/or the maintenanceof the cells in serum free medium as soon as the saturation density atwhich no further replication occurs is obtained. The term “cultivationof cells” in a serum free medium refers to a method in which all of theabove mentioned steps are performed with serum free medium, so that noanimal serum products are present during the whole cultivation of thecells. The media used in all of the above steps may preferably comprisea factor selected from the group of growth factors. However, it might besufficient to add such a factor only to the media used for the seedingof the cells and/or the growing of the cells under logarithmicconditions. As explained below in more detail it might also be possibleto cultivate cells that would normally grow as attached cells also assuspension culture cells if appropriate incubation conditions are chosen(e.g. by applying “wave” incubation). The method according to thepresent invention also applies for this type of incubation.

The term “serum-free” medium refers to any cell culture medium that doesnot contain sera from animal or human origin. Suitable cell culturemedia are known to the person skilled in the art. These media comprisesalts, vitamins, buffers, energy sources, amino acids and othersubstances. An example of a medium suitable for the serum freecultivation of CEF cells is medium 199 (Morgan, Morton and Parker; Proc.Soc. Exp. Biol. Med. 1950, 73, 1; obtainable inter alia fromLifeTechnologies).

The media used according to the method of the present invention, inparticular the media used for adherent cells such as CEF cells, containa factor selected from the group consisting of growth factors andattachment factors. An example of an attachment factor is fibronectin.

For cells that naturally grow as adherent cells, which, however, arenevertheless cultivated in suspension culture (which is possible e.g.for CEF cells), it is a further aspect of the invention to use a factorselected from growth factors. Examples of growth factors useful for thistype of cultivation are recombinant bovine, mouse, chicken, humanepidermal growth factor (EGF), particularly recombinant human EGF(rh-EGF) (Chemicon Int., catalog number: GF001).

For cells naturally growing in suspension culture the medium maycomprise a factor selected from the group of growth factors includingEGF. Growth factors for these types of cells are factors specific fornon-adherent cells. Examples of these growth factors are interleukins,GM-CSF, G-CSF and others. The person skilled in the art may easilydetermine by routine experimentation, which type of factor is suitablefor which type of cells.

If the factor added to the serum free medium is EGF, in particularrh-EGF, it is an aspect of the invention to add such growth factor tothe medium at a concentration of 1 to 50 ng/ml. It is a further aspectto add such factor at a concentration of 5 to 20 ng/ml. However, theperson skilled in the art will be aware of the fact that different celltypes may require a somewhat different concentration of EGF in themedium for optimal results.

If the attachment factor added to the serum free medium is fibronectin:(e.g. Chemicon Int.; Human plasma fibronectin; catalog number FC010), itis an aspect of the invention to add such factor to the medium at aconcentration of 1 to 50. It is a further aspect to add such factor at aconcentration of 1 to 10 μg/cm² surface of the cell culture vessel.However, those skilled in the art understand that different cell typesmay require a somewhat different concentration of fibronectin in themedium for optimal results.

It is sufficient to add only one factor selected from growth factors andattachment factors to the medium, in particular if the cells areadherent cells. However, it is also possible to add two or more factorsselected from growth factors and attachment factors to the medium. Themedium may comprise EGF and fibronectin, possibly in the concentrationranges defined above, in particular if the primary cells are adherentcells such as CEF cells.

The medium may further comprise one or more additives selected frommicrobial extracts, plant extracts and extracts from non-mammaliananimals. The microbial extract may be a yeast extract or yeastolateultrafiltrate. The plant extract may be a rice extract or soya extract.The extract from non-mammalian animals may be a fish extract.

Asparagine may also be added to the commercially available serum freemedium to which a factor selected from growth factors and attachmentfactors has been added. Asparagine may also be added to the medium thatis used during the infection with virus (see below). Commercial serumfree media usually comprise asparagine in a concentration range of 0.3to 1.0 mM. It is an aspect of the invention to add asparagine tosupplement the medium in the range of 0.5 to 1.5 mM. A 1 mM asparaginesupplement may be adequate. The total concentration of asparagine in themedium is less than 2 mM, in the range of 0.8 to 1.8 mM. For example,the concentration of asparagine in the medium is 1.3 mM.

Moreover, glutamine may also be added to the medium. Glutamine may alsobe added to the medium that is used during the infection with virus (seebelow). Glutamine may also be added to supplement the medium atconcentrations in the range of 1 to 5 mM. It is a further aspect of theinvention to add glutamine at a concentration in the range of 2 to 4 mM.The indicated ranges also correspond to the total concentrations in themedium since most of the commercially available media do not containglutamine.

Amplification of a virus may comprise the following steps: in the firststep primary cells are cultivated according to the method describedabove, i.e. primary cells are cultivated in a serum free mediumcomprising a factor selected from the group consisting of growth factorsand attachment factors, depending on the cell type. All conditions anddefinitions given in the description of the method for the cultivationof primary cells above also apply to the definition of the first step ofthe method for the amplification of virus according to this embodimentof the present invention. In a second step the primary cells areinfected with the virus. In the third step the infected cells areincubated in serum free medium until progeny virus is produced. Finally,in a fourth step, the virus is isolated from infected cells.

The term “amplification of a virus” is used to make clear that themethod according to the present invention is typically used to increasethe amount of virus due to a productive viral replication of the virusin the infected cells. In other words the ratio of output virus to inputvirus should be above 1. Primary cells are chosen for a specific virusin which the virus is able to productively replicate. The term“reproductive replication” refers to the fact that the specific virusreplicates in the specific primary cell to such an extent thatinfectious progeny virus is produced, wherein the ratio of output virusto input virus is above 1.

The selection of primary cell type which supports productive replicationof a particular virus is known. By way of example the primary cells maybe human foreskin fibroblasts if the virus to be amplified is the humanCytomegalovirus; the primary cells may be CEF cells if the virus to beamplified is measles virus, mumps virus, rabies virus, Japaneseencephalitis virus, yellow fever virus, influenza virus or a poxvirussuch as vaccinia virus.

Methods for infecting primary cells according to the second step ofinstant method for virus amplification are known. By way of example thevirus may simply be added to the medium. Alternatively, the medium maybe removed and the virus may be added to fresh medium, which in turn isadded to the cells. To obtain an efficient infection the amount of thevirus/medium suspension should be as low as possible to have a highvirus concentration. After the attachment of the virus additional mediummay be added.

In the third step of the instant method, the infected cells arecultivated in serum free medium until progeny virus is produced.

The serum free medium that is used in the second and third step of themethod for the amplification of a virus may be the same medium that hasalready been used before, i.e. a serum free medium comprising a factorselected from growth factors and attachment factors, depending on thecell type. Alternatively, the serum free medium comprising growthfactors and attachment factors may be removed at the step of infectingthe primary avian cells with the virus, and/or at the step ofcultivating the infected cells until virus progeny is produced, andreplaced with a serum free medium which is essentially free of growthfactors and attachment factors without adverse effects on the culture.

During all stages the medium may be supplemented with asparagine and/orglutamine as outlined above, wherein the total concentration ofasparagine in the medium is as defined above.

The progeny virus may be concentrated and purified according to methodsknown to the person skilled in the art.

Thus, the present invention relates to a method for the amplification ofa poxvirus comprising the following steps: (I) cultivating primary cellsaccording to a method as described above, i.e. a method in which theprimary cells are cultivated in serum free medium comprising a factorselected from the group consisting of growth factors and attachmentfactors, depending on the cell type, (II) infecting the primary cellswith the poxvirus, (III) cultivating the infected cells in serum freemedium until progeny virus is produced and (iv) isolating the virus fromthe infected cells. Viruses isolated according to the instant method arefree of any products and/or infectious agents comprised in animal sera.

The process of passaging and/or further cultivating and/or plaquepurifying and/or purifying by limited dilution or any other method underserum free conditions those viruses that previously have been or mayhave been amplified under serum containing conditions is termed“re-derivation”. A re-derivation under serum-free conditions drasticallyreduces the risk of contaminations in the vaccine, in particular ofundesired infectious agents.

The methods according to the present invention relate to cultivatingprimary avian cells and to amplifying a virus, wherein the virus is thevirus that is to be re-derived. For example, the instant methods areuseful for the re-derivation of viruses and virus stocks, in particularfor stocks that have been, or may have been passaged in serum containingmedium and/or with unclear passage histories.

One passage of the starting material, i.e. of the virus to be re-derivedunder serum free conditions, may be sufficient for the re-derivation ofa virus. The term “passaging” refers to the steps of cultivating cellsunder serum free conditions, infection of the cells with the virus to bere-derived and obtaining the virus produced in the infected cells.Although one passage might be sufficient, it may be preferable topassage the virus several times under serum free conditions. In thiscase the virus obtained from the first passaging step is used to againinfect fresh cells. The passaging under serum free conditions may becombined with one or more plaque purifications and/or with limiteddilution and/or any other method for the purification of a virus underserum free conditions. The total number of passages, optionally byincluding plaque purification and/or limited dilution is in a range of 1to more than 10, such as 3 to 8 or 4 to 6. The techniques of plaquepurification and/or limited dilution are standard virological methodspracticed by those skilled in the art.

The re-derivation according to the present invention may be done with avirus starting material that exhibits desired biological properties,wherein the virus used as starting material may have been amplifiedunder serum containing conditions. After several passages under serumfree conditions according to the present invention it is confirmedwhether the virus passaged under serum free conditions isidentical/similar to the virus originally passaged under serumcontaining methods. In most cases the virus obtained after there-derivation has similar/identical properties to the virus used asstarting material. There may also be situations in which the re-derivedvirus has even improved properties compared to the virus used asstarting material, e.g. an improved safety profile.

The present invention also relates to the re-derived virus obtained bythe method according to the present invention. The risk that poxvirusobtained by the re-derivation method according to the present inventioncomprises a BSE particle is less than 10³².

If it is intended to re-derive a virus, the following re-derivation planmay be used by way of example. This plan is particularly suitable forthe re-derivation of a Vaccinia virus, e.g. an MVA strain that has ormay have been cultivated under serum containing conditions: First theoriginal Master Virus Bank (MVB) virus seed stock is re-cloned through,for example, 5 rounds of plaque purification by limited dilution (seeexample 9). Viruses from the original virus seed stock and from the newre-derived stock are compared both genetically and phenotypically. Agenetic comparison of the virus cultivated under serum containingconditions and the re-derived virus may be made by, for example, (i)Restriction Enzyme mapping of the viral genome (RE-Map), (ii) PCRamplification of relevant parts of the genome such as the six deletionsites in case on MVA and/or (iii) PCR based restriction fragment lengthpolymorphism mapping of the viral genome (PCR-RFLP Assay). A phenotypiccharacterization may, for example, be performed by: (i) comparinghumoral responses in vaccinated mice, (ii) comparing efficacy using alethal vaccinia model, (iii) evaluating safety by the vaccination ofseverely immune compromised mice, (iv) comparing the attenuation(replication) in a variety of mammalian cell lines.

The present invention consequently relates to a re-derivation processnamely the method for the cultivation of primary avian cells as definedabove and/or the method for the amplification of a virus as definedabove, wherein the virus is the virus that is to be re-derived. Theinvention further relates to re-derived virus such as re-derivedVaccinia viruses, e.g. MVA strains such as MVA-BN. The re-derived viruscan be e.g. a re-derived wild type virus, a re-derived attenuated virusor a re-derived recombinant virus. The invention further relates tocompositions comprising re-derived virus.

The invention further relates to a virus including a re-derived virus,in particular to the viruses including the re-derived viruses as definedabove as a medicament or vaccine. If the virus is a wild-type virus oran attenuated virus the virus can be used for vaccination against thevirus as such. For this purpose attenuated viruses are particularlypreferred. If the virus is a recombinant virus expressing proteinsexpressed from genes heterologous to the viral genome, it is possible tovaccinate against the virus as such and/or against the expressedheterologous protein. If the recombinant virus expresses a therapeuticgene such as an antisense RNA or a ribozyme the virus may be used as amedicament.

As discussed previously, it is understood by those skilled in the artthat primary avian cells grow adversely under serum free conditions. Theadditional stress associated with a poxvirus infection may be expectedto cause the already stressed cells to die before a significantamplification of the poxvirus occurs. Surprisingly, avian cells grownaccording to the present method, in a serum free medium comprising afactor selected from growth factors and attachment factors, effectivelysupport viral replication and amplification of poxviruses.

The poxvirus is preferably an orthopoxvirus. Examples of orthopoxviruses are avipoxviruses and vaccinia viruses.

The term “avipoxvirus” refers to any avipoxvirus, such as Fowlpoxvirus,Canarypoxvirus, Uncopoxvirus, Mynahpoxvirus, Pigeonpoxvirus,Psittacinepoxvirus, Quailpoxvirus, Peacockpoxvirus, Penguinpoxvirus,Sparrowpoxvirus, Starlingpoxvirus and Turkeypoxvirus. Preferredavipoxviruses are Canarypoxvirus and Fowlpoxvirus.

An example of a canarypox virus is strain Rentschler. A plaque purifiedCanarypox strain termed ALVAC (U.S. Pat. No. 5,766,598) was depositedunder the terms of the Budapest treaty with the American Type CultureCollection (ATCC), accession number VR-2547. Another Canarypox strain isthe commercial canarypox vaccine strain designated LF2 CEP 524 24 10 75,available from Institute Merieux, Inc.

Examples of a Fowlpox virus are strains FP-1, FP-5 and TROVAC (U.S. Pat.No. 5,766,598). FP-1 is a Duvette strain modified to be used as avaccine in one-day old chickens. The strain is a commercial fowlpoxvirus vaccine strain designated O DCEP 25/CEP67/2309 October 1980 and isavailable from Institute Merieux, Inc. FP-5 is a commercial fowlpoxvirus vaccine strain of chicken embryo origin available from AmericanScientific Laboratories (Division of Schering Corp.) Madison, Wis.,United States Veterinary License No. 165, serial No. 30321.

Examples of vaccinia virus strains are the strains Temple of Heaven,Copenhagen, Paris, Budapest, Dairen, Gam, MRIVP, Per, Tashkent, TBK,Tom, Bern, Patwadangar, BIEM, B-15, Lister, EM-63, New York City Boardof Health, Elstree, Ikeda and WR. The invention is preferably carriedout with modified vaccinia virus Ankara (MVA) (Sutter, G. et al. [1994],Vaccine 12: 1032-40). Typical MVA strains are MVA 575 that has beendeposited at the European Collection of Animal Cell Cultures under thedeposition number ECACC V00120707 and MVA-572 deposited at ECACC underthe deposition number V94012707. MVA-BN has been deposited at theEuropean Collection of Animal Cell Cultures with the deposition numberECACC V00083008.

The virus to be amplified according to the method of the presentinvention may be a wild-type virus, an attenuated virus or a recombinantvirus.

As pointed out above, for poxviruses the primary cells may be primaryavian cells such as CEF cells or primary duck embryo fibroblasts. Again,one skilled in the art understands which primary cells are suitable forthe amplification of which poxvirus. CEF cells are known for theamplification of MVA. If the method according to the present inventionis used for the amplification of MVA in CEF cells, the starting pH ofthe medium may be in a range of about 7.0 to about 8.5. For MVAamplification in CEF cells in serum free medium, it is an aspect of theinvention to select one or two of the factors selected from EGF andfibronectin.

The invention also relates to vaccinia virus strains obtained by themethod of the present invention, in particular MVA-BN and itsderivatives, which are further characterized by a failure to replicatein vivo. In the context of the present invention, “failure to replicatein vivo” refers to viruses that do not replicate in humans and in themouse model described below. The “failure to replicate in vivo” can bedetermined in mice that are incapable of producing mature B and T cells.An example of such mice is the transgenic mouse model AGR129 (obtainedfrom Mark Sutter, Institute of Virology, University of Zurich, Zurich,Switzerland). This mouse strain has targeted gene disruptions in the IFNreceptor type I (IFN-α/β) and type II (IFN-γ) genes, and in RAG. Due tothese disruptions, the mice have no IFN system and are incapable ofproducing mature B and T cells, and as such, are severelyimmune-compromised and highly susceptible to a replicating virus. Inaddition to the AGR129 mice, any other mouse strain may be used that isincapable of producing mature B and T cells, and as such, is severelyimmune-compromised and highly susceptible to a replicating virus. Theviruses of the present invention do not kill AGR129 mice within a timeperiod on the average of at least 45 days, and up to at least 60 days,and to 90 days post infection of the mice with 10⁷ pfu virusadministered via intra-peritoneal injection. The viruses that exhibit“failure to replicate in vivo” are further characterized in that novirus can be recovered from organs or tissues of the AGR129 mice on theaverage of 45 days, 60 days, and even 90 days after infection of themice with 10⁷ pfu virus administered via intra-peritoneal injection.Detailed information regarding the infection assays using AGR129 miceand the assays used to determine whether virus may be recovered fromorgans and tissues of infected mice can be found in the example section.

In a further embodiment, the vaccinia virus strains of the invention, inparticular MVA-BN and its derivatives, are characterized as inducing ahigher specific immune response compared to the strains MVA 575 and MVA572, as determined in a lethal challenge mouse model. Briefly, in such amodel unvaccinated mice die after infection with replication competentvaccinia strains such as the Western Reserve strain L929 TK+ or IHD-J.Infection with replication competent vaccinia viruses is referred to as“challenge” in the context of description of the lethal challenge model.Four days after the challenge, the mice are usually killed and the viraltiter in the ovaries is determined by standard plaque assays using VEROcells (for more details see example section). The viral titer isdetermined for unvaccinated mice and for mice vaccinated with vaccinaviruses of the present invention. More specifically, the viruses of thepresent invention are characterized in that, in this test after thevaccination with 10² TCID₅₀/ml of virus of the present invention, theovarian virus titers are reduced by at least an average of 70%, 80%, andeven 90%, compared to unvaccinated mice.

In a further embodiment, the vaccinia viruses of the present invention,in particular MVA-BN and its derivatives, are useful for immunizationwith prime/boost administration of the vaccine. There have been numerousreports suggesting that prime/boost regimes using a known MVA as adelivery vector induce poor immune responses and are inferior toDNA-prime/ MVA-boost regimes (Schneider et al., 1998, Nat. Med. 4;397-402). In all of these studies the MVA strains that have been usedare different from the vaccinia viruses of the present invention. Toexplain the poor immune response when MVA was used for prime and boostadministration, it has been hypothesized that antibodies generated toMVA during the prime-administration neutralized the MVA administered inthe second immunization, thereby preventing an effective boost of theimmune response. In contrast, DNA-prime/MVA-boost regimes are reportedto be superior in generating high avidity responses because this regimecombines the ability of DNA to effectively prime the immune responsewith the properties of MVA to boost the response in the absence of apre-existing immunity to MVA.

Clearly, if a pre-existing immunity to MVA and/or vaccinia preventsboosting of the immune response, then the use of MVA as a vaccine ortherapeutic would have limited efficacy, particularly in the individualsthat have been previously vaccinated against smallpox. However, thevaccinia virus of the present invention, in particular MVA-BN and itsderivatives, as well as corresponding recombinant viruses harboringheterologous sequences, can be used to efficiently first prime and thenboost immune responses in naive animals, as well as animals with apre-existing immunity to poxviruses. Thus, the vaccinia virus of thepresent invention induces at least substantially the same level ofimmunity in vaccinia virus prime/vaccinia virus boost regimes comparedto DNA-prime/vaccinia virus boost regimes.

The term “animal” as used in the present description is intended to alsoinclude human beings. Thus, the virus of the present invention is alsouseful for prime/boost regimes in human beings. If the virus is anon-recombinant virus such as MVA-BN or a derivative thereof, the virusmay be used as a smallpox vaccine in humans, wherein the same virus canbe used in both the priming and boosting vaccination. If the virus is arecombinant virus such as MVA-BN or a derivative thereof that encodes aheterologous antigen, the virus may be used in humans as a vaccineagainst the agent from which the heterologous antigen is derived,wherein the same virus can be used in both the priming and boostingvaccination.

A vaccinia virus is regarded as inducing at least substantially the samelevel of immunity in vaccinia virus prime/vaccinia virus boost regimesif, when compared to DNA-prime/vaccinia virus boost regimes, the CTLresponse, as measured in one of the following two assays (“assay 1” and“assay 2”), preferably in both assays, is at least substantially thesame in vaccinia virus prime/vaccinia virus boost regimes when comparedto DNA-prime/vaccinia virus boost regimes. More preferably, the CTLresponse after vaccinia virus prime/vaccinia virus boost administrationis higher in at least one of the assays, when compared toDNA-prime/vaccinia virus boost regimes. Most preferably, the CTLresponse is higher in both of the following assays.

Assay 1: For vaccinia virus prime/vaccinia virus boost administrations,6-8 week old BALB/c (H-2d) mice are prime-immunized by intravenousadministration with 10⁷ TCID₅₀ vaccinia virus of the inventionexpressing the murine polytope as described in Thomson et al., 1998, J.Immunol. 160, 1717 and then boost-immunized with the same amount of thesame virus, administered in the same manner three weeks later. To thisend, it is necessary to construct a recombinant vaccinia virusexpressing the polytope. Methods to construct such recombinant virusesare known to a person skilled in the art and are described in moredetail below. In DNA prime/vaccinia virus boost regimes the primevaccination is done by intra muscular injection of the mice with 50 μgDNA expressing the same antigen as the vaccinia virus. The boostadministration with the vaccinia virus is done in exactly the same wayas for the vaccinia virus prime/vaccinia virus boost administration. TheDNA plasmid expressing the polytope is also described in the publicationreferenced above, i.e., Thomson, et al. In both regimes, the developmentof a CTL response against the epitopes SYI, RPQ and/or YPH is determinedtwo weeks after the boost administration. The determination of the CTLresponse is preferably done using the ELISPOT analysis as described bySchneider, et al., 1998, Nat. Med. 4, 397-402, and as outlined in theexamples section below for a specific virus of the invention. The virusof the invention is characterized in this experiment in that the CTLimmune response against the epitopes mentioned above, which is inducedby the vaccinia virus prime/vaccinia virus boost administration, issubstantially the same, preferably at least the same, as that induced byDNA prime/vaccinia virus boost administration, as assessed by the numberof IFN-γ producing cells/10⁶ spleen cells (see also experimentalsection).

Assay 2: This assay basically corresponds to assay 1. However, insteadof using 10⁷ TCID₅₀ vaccinia virus administered i.v., as in Assay 1; inAssay 2, 10⁸ TCID₅₀ vaccinia virus of the present invention isadministered by subcutaneous injection for both prime and boostimmunization. The virus of the present invention is characterized inthis experiment in that the CTL immune response against the epitopesmentioned above, which is induced by the vaccinia virus prime/vacciniavirus boost administration, is substantially the same, preferably atleast the same, as that induced by DNA prime/vaccinia virus boostadministration, as assessed by the number of IFN-γ producing cells/10⁶spleen cells (see also experimental section).

In summary, a representative vaccinia virus of the present invention ischaracterized by having at least one of the following properties:

-   -   capability of reproductive replication in chicken embryo        fibroblasts (CEF), but no capability of reproductive replication        in a human cell line known to permit replication with known        vaccinia strains,    -   failure to replicate in vivo in those animals, including humans,        in which the virus is used as a vaccine or active ingredient of        a pharmaceutical composition,    -   induction of a higher specific immune response compared to a        known vaccinia strain,    -   induction of at least substantially the same level of a specific        immune response in vaccinia virus prime/vaccinia virus boost        regimes when compared to DNA-prime/vaccinia virus boost regimes,        and/or    -   may or may not have the additional characteristic of        reproductive replication in CEF cells grown in serum free        medium.

Preferably, the vaccinia virus of the present invention has at least twoof the above properties, and more preferably at least three of the aboveproperties. Most preferred are vaccinia viruses having all of the aboveproperties.

Representative vaccinia virus strains are MVA 575 deposited on Dec. 7,2000 at the European Collection of Animal Cell Cultures (ECACC) with thedeposition number V00120707; MVA-572 deposited at ECACC under thedeposition number V94012707; and MVA-BN, deposited on Aug. 30, 2000, atECACC with the deposition number V000083008, and derivatives thereof, inparticular if it is intended to vaccinate/treat humans. MVA-BN and itsderivatives are most preferred for humans.

In a further embodiment, the invention concerns a kit for vaccinationcomprising a virus of the present invention for the first vaccination(“priming”) in a first vial/container and for a second vaccination(“boosting”) in a second vial/container. The virus may be anon-recombinant vaccinia virus, i.e., a vaccinia virus that does notcontain heterologous nucleotide sequences. An example of such a vacciniavirus is MVA-BN and its derivatives. Alternatively, the virus may be arecombinant vaccinia virus that contains additional nucleotide sequencesthat are heterologous to the vaccinia virus. As outlined in othersections of the description, the heterologous sequences may code forepitopes that induce a response by the immune system. Thus, it ispossible to use the recombinant vaccinia virus to vaccinate against theproteins or agents comprising the epitope. The viruses may be formulatedas shown below in more detail. The amount of virus that may be used foreach vaccination has been defined above.

A process for obtaining a virus of the instant invention may comprisethe following steps:

-   -   I. introducing a vaccinia virus strain, into non-human cells in        which the virus is able to reproductively replicate, wherein the        non-human cells are preferably selected from CEF cells,    -   II. isolating/enriching virus particles from these cells and    -   III. analyzing whether the obtained virus has at least one of        the desired biological properties as previously defined above,        wherein the above steps can optionally be repeated until a virus        with the desired replication characteristics is obtained. The        invention further relates to the viruses obtained by the method        of the instant invention. Moreover, the invention pertains to        such virus cultured in serum free media. Methods for determining        the expression of the desired biological properties are        explained in other parts of this description.

The growth behavior of the vaccinia viruses of the present invention, inparticular the growth behavior of MVA-BN, indicates that the strains ofthe present invention are far superior to any other characterized MVAisolates in terms of attenuation in human cell lines and failure toreplicate in vivo. The strains of the present invention are thereforeideal candidates for the development of safer products such as vaccinesor pharmaceuticals, as described below.

In one further embodiment, the virus of the present invention, inparticular MVA-BN and its derivatives, is used as a vaccine againsthuman poxvirus diseases, such as smallpox.

In a further embodiment, the virus of the present invention may berecombinant, i.e., may express heterologous genes as, e.g., antigens orepitopes heterologous to the virus, and may thus be useful as a vaccineto induce an immune response against heterologous antigens or epitopes.

The term “immune response” means the reaction of the immune system whena foreign substance or microorganism enters the organism. By definition,the immune response is divided into a specific and an unspecificreaction although both are closely related. The unspecific immuneresponse is the immediate defence against a wide variety of foreignsubstances and infectious agents. The specific immune response is thedefence raised after a lag phase, when the organism is challenged with asubstance for the first time. The specific immune response is highlyefficient and is responsible for the fact that an individual whorecovers from a specific infection is protected against this specificinfection. Thus, a second infection with the same or a very similarinfectious agent causes much milder symptoms or no symptoms at all,since there is already a “pre-existing immunity” to this agent. Suchimmunity and immunological memory persist for a long time, in some caseseven lifelong. Accordingly, the induction of an immunological memory canbe used for vaccination.

The “immune system” means a complex organ involved in the defence of theorganism against foreign substances and microorganisms. The immunesystem comprises a cellular component, comprising several cell types,such as, e.g., lymphocytes and other cells derived from white bloodcells, and a humoral component, comprising small peptides and complementfactors.

“Vaccination” means that an organism is challenged with an infectiousagent, e.g., an attenuated or inactivated form of the infectious agent,to induce a specific immunity. The term vaccination also covers thechallenge of an organism with recombinant vaccinia viruses of thepresent invention, in particular recombinant MVA-BN and its derivatives,expressing antigens or epitopes that are heterologous to the virus.Examples of such epitopes are provided elsewhere in the description andinclude e.g., epitopes from proteins derived from other viruses, such asthe Dengue virus, Hepatitis C virus, HIV, or epitopes derived fromproteins that are associated with the development of tumors and cancer.Following administration of the recombinant vaccinia virus, the epitopesare expressed and presented to the immune system. A specific immuneresponse against these epitopes may be induced. The organism, thus, isimmunized against the agent/protein containing the epitope that isencoded by the recombinant vaccinia virus.

“Immunity” means partial or complete protection of an organism againstdiseases caused by an infectious agent due to a successful eliminationof a preceding infection with the infectious agent or a characteristicpart thereof. Immunity is based on the existence, induction, andactivation of specialized cells of the immune system.

As indicated above, in one embodiment of the invention the recombinantviruses of the present invention, in particular recombinant MVA-BN andits derivatives, contain at least one heterologous nucleic acidsequence. The term “heterologous” is used hereinafter for anycombination of nucleic acid sequences that is not normally foundintimately associated with the virus in nature; such virus is alsocalled a “recombinant virus”.

According to a further embodiment of the present invention, theheterologous sequences are antigenic epitopes that are selected from anynon-vaccinia source. The recombinant virus may express one or moreantigenic epitopes from: Plasmodium falciparum, bacteria, includingmycobacteria, influenza virus, viruses of the family of flaviviruses,paramyxoviruses, hepatitis viruses, human immunodeficiency viruses, orfrom viruses causing hemorrhagic fever, such as hantaviruses orfiloviruses, i.e., ebola or marburg virus.

According to still a further embodiment, but also in addition to theabove-mentioned selection of antigenic epitopes, the heterologoussequences may be selected from another poxviral or a vaccinia source.These viral sequences can be used to modify the host spectrum or theimmunogenicity of the virus.

In a further embodiment the virus of the present invention may code fora heterologous gene/nucleic acid expressing a therapeutic compound. A“therapeutic compound” encoded by the heterologous nucleic acid in thevirus can be, e.g., a therapeutic nucleic acid, such as an antisensenucleic acid, including an antisense expression cassette or a ribozymegene, or a peptide or protein with desired biological activity, or agene coding for a peptide comprising at least one epitope to induce animmune response.

According to a further embodiment, the expression of a heterologousnucleic acid sequence may be, but not exclusively, under thetranscriptional control of a poxvirus promoter, possibly a vacciniavirus promoter.

According to still a further embodiment, the heterologous nucleic acidsequence is inserted into a non-essential region of the virus genome. Inanother embodiment of the invention, the heterologous nucleic acidsequence is inserted at a naturally occurring deletion site of the MVAgenome as disclosed in PCT/EP96/02926 the subject matter of which ishereby incorporated by reference. Methods for inserting heterologoussequences into the poxviral genome are known to a person skilled in theart.

According to yet another embodiment, the invention also includes thegenome of the virus, its recombinants, or functional parts thereof. Suchviral sequences can be used to identify or isolate the virus or itsrecombinants, e.g., by using PCR, hybridization technologies, or byestablishing ELISA assays. Furthermore, such viral sequences can beexpressed from an expression vector to produce the encoded protein orpeptide that then may supplement deletion mutants of a virus that lacksthe viral sequence contained in the expression vector.

“Functional part” of the viral genome means a part of the completegenomic sequence that encodes a physical entity, such as a protein,protein domain, or an epitope of a protein. Functional part of the viralgenome also describes parts of the complete genomic sequence that codefor regulatory elements or parts of such elements with individualizedactivity, such as promoter, enhancer, cis- or trans-acting elements.

The recombinant virus of the present invention may be used for theintroduction of a heterologous nucleic acid sequence into a target cell,the sequence being either homologous or heterologous to the target cell.The introduction of a heterologous nucleic acid sequence into a targetcell may be used to produce in vitro heterologous peptides orpolypeptides, and/or complete viruses encoded by the sequence. Thismethod comprises the infection of a host cell with the recombinant MVA;cultivation of the infected host cell under suitable conditions; andisolation and/or enrichment of the peptide, protein and/or virusproduced by the host cell.

Furthermore, the method for introduction of a homologous or heterologoussequence into cells may be applied for in vitro and preferably in vivotherapy. For in vitro therapy, isolated cells that have been previously(ex vivo) infected with the virus are administered to a living animalbody for inducing an immune response. For in vivo therapy, the virus orits recombinants are directly administered to a living animal body toinduce an immune response. In this case, the cells surrounding the siteof inoculation are directly infected in vivo by the virus, or itsrecombinants, of the present invention.

Since the virus of the invention is highly growth restricted in humanand monkey cells and thus, highly attenuated, it is ideal to treat awide range of mammals, including humans. Hence, the present inventionalso provides a pharmaceutical composition and a vaccine, e.g., forinducing an immune response in a living animal body, including a human.The virus of the invention is also safe in any other gene therapyprotocol.

A pharmaceutical composition may generally include one or morepharmaceutical acceptable and/or approved carriers, additives,antibiotics, preservatives, adjuvants, diluents and/or stabilizers. Suchauxiliary substances can be water, saline, glycerol, ethanol, wetting oremulsifying agents, pH buffering substances, or the like. Suitablecarriers are typically large, slowly metabolized molecules such asproteins, polysaccharides, polylactic acids, polyglycolic acids,polymeric amino acids, amino acid copolymers, lipid aggregates, or thelike.

For the preparation of vaccines, the virus or a recombinant of thepresent invention, is converted into a physiologically acceptable form.This can be done based on experience in the preparation of poxvirusvaccines used for vaccination against smallpox (as described by Stickl,H. et al. [1974] Dtsch. med. Wschr. 99, 2386-2392). For example, thepurified virus is stored at −80° C. with a titer of 5×10⁸ TCID₅₀/mlformulated in about 10 mM Tris, 140 mM NaCl, pH 7.4. For the preparationof vaccine shots, e.g., 10²-10⁸ particles of the virus are lyophilizedin 100 ml of phosphate-buffered saline (PBS) in the presence of 2%peptone and 1% human albumin in an ampoule, preferably a glass ampoule.Alternatively, the vaccine shots can be produced by stepwise,freeze-drying of the virus in a formulation. This formulation cancontain additional additives such as mannitol, dextran, sugar, glycine,lactose, polyvinylpyrrolidone, or other additives, such as antioxidantsor inert gas, stabilizers or recombinant proteins (e.g. human serumalbumin) suitable for in vivo administration. The glass ampoule is thensealed and can be stored between 4° C. and room temperature for severalmonths. However, as long as no need exists the ampoule is storedpreferably at temperatures below −20° C.

For vaccination or therapy, the lyophilisate can be dissolved in 0.1 to0.5 ml of an aqueous solution, preferably physiological saline or Trisbuffer, and administered either systemically or locally, i.e., byparenteral, intramuscular, or any other path of administration known toa skilled practitioner. The mode of administration, dose, and number ofadministrations can be optimized by those skilled in the art in a knownmanner.

Additionally according to a further embodiment, the virus of the presentinvention is particularly useful to induce immune responses inimmune-compromised animals, e.g., monkeys (CD4<400/μl of blood) infectedwith SIV, or immune-compromised humans. The term “immune-compromised”describes the status of the immune system of an individual that exhibitsonly incomplete immune responses or has a reduced efficiency in thedefence against infectious agents. Even more interesting and accordingto still a further embodiment, the virus of the present invention canboost immune responses in immune-compromised animals or humans even inthe presence of a pre-existing immunity to poxvirus in these animals orhumans. Of particular interest, the virus of the present invention canalso boost immune responses in animals or humans receiving an antiviral,e.g., antiretroviral therapy. “Antiviral therapy” includes therapeuticconcepts in order to eliminate or suppress viral infection including,e.g., (i) the administration of nucleoside analogs, (ii) theadministration of inhibitors for viral enzymatic activity or viralassembling, or (iii) the administration of cytokines to influence immuneresponses of the host.

According to still a further embodiment, the vaccine is especially, butnot exclusively, applicable in the veterinary field, e.g., immunizationagainst animal pox infection. In small animals, the immunizinginoculation is preferably administered by nasal or parenteraladministration, whereas in larger animals or humans, a subcutaneous,oral, or intramuscular inoculation is preferred.

A vaccine shot containing an effective dose of only 10² TCID₅₀ (tissueculture infectious dose) of the virus of the present invention issufficient to induce complete immunity against a wild type vacciniavirus challenge in mice. This is particularly surprising since such ahigh degree of attenuation of the virus of the present invention wouldbe expected to negatively influence and thereby, reduce itsimmunogenicity. Such expectation is based on the understanding that forinduction of an immune response, the antigenic epitopes must bepresented to the immune system in sufficient quantity. A virus that ishighly attenuated and thus, not replicating, can only present a verysmall amount of antigenic epitopes, i.e., as much as the virus itselfincorporates. The amount of antigen carried by viral particles is notconsidered to be sufficient for induction of a potent immune response.However, the virus of the invention stimulates, even with a very loweffective dose of only 10² TCID₅₀, a potent and protective immuneresponse in a mouse/vaccinia challenge model. Thus, the virus of thepresent invention exhibits an unexpected and increased induction of aspecific immune response compared to other characterized MVA strains.This makes the virus of the present invention and any vaccine derivedthereof, especially useful for application in immune-compromised animalsor humans.

According to still another embodiment of the invention, the virus isused as an adjuvant. An “adjuvant” in the context of the presentdescription refers to an enhancer of the specific immune response invaccines. “Using the virus as adjuvant” means including the virus in apre-existing vaccine to additionally stimulate the immune system of thepatient who receives the vaccine. The immunizing effect of an antigenicepitope in most vaccines is often enhanced by the addition of aso-called adjuvant. An adjuvant co-stimulates the immune system bycausing a stronger specific immune reaction against an antigenic epitopeof a vaccine. This stimulation can be regulated by factors of theunspecific immune system, such as interferon and interleukin. Hence, ina further embodiment of the invention, the virus is used in mammals,including humans, to activate, support, or suppress the immune system,and preferably to activate the immune response against any antigenicdeterminant. The virus may also be used to support the immune system ina situation of increased susceptibility to infection, such as in thecase of stress.

The virus used as an adjuvant may be a non-recombinant virus, i.e., avirus that does not contain heterologous DNA in its genome. An exampleof this type of virus is MVA-BN. Alternatively, the virus used as anadjuvant is a recombinant virus containing in its genome heterologousDNA sequences that are not naturally present in the viral genome. Foruse as an adjuvant, the recombinant viral DNA preferably contains andexpresses genes that code for immune stimulatory peptides or proteinssuch as interleukins.

According to a further embodiment, it is preferred that the virus isinactivated when used as an adjuvant or added to another vaccine. Theinactivation of the virus may be performed by e.g., heat or chemicals,as known in the art. Preferably, the virus is inactivated byβ-propriolacton. According to this embodiment of the invention, theinactivated virus may be added to vaccines against numerous infectiousor proliferative diseases to increase the immune response of the patientto this disease.

EXPERIMENTAL PART

The present invention will be better understood in connection with thefollowing examples, which are intended as an illustration of and not alimitation upon the scope of the invention.

EXAMPLE 1 Preparation of Chicken Embryo Fibroblast (CEF) Cells

Specific pathogen free (SPF) fertilized eggs were stored not longer than12 days at 4° C. The eggs were put into an incubator and incubated for10-12 days at 37.8° C.±8° C. One petri dish per maximum 11 eggs wasprepared with 10-20 ml PBS. The eggs were put in a dedicated egg cartonand treated extensively with Bacillol® to sterilize the outside of theegg shell. After drying, a hole was made into the eggs and the shell wasremoved carefully. The chorioallantoic membrane was put aside. Theembryos were lifted up by the feet and then their heads were cut off.The embryos were then transferred into the prepared petri dishes. Afterremoving the feet the trunks were washed again with PBS. 11 trunksmaximum were put into a 20 ml plastic syringe and squeezed into anErlenmeyer flask. 5 ml of prewarmed (37° C.) Trypsin/EDTA-solution pertrunk were added and the solution was stirred for 15 minutes with serumfree medium at room temperature using a magnetic stirrer. Trypsinizedcells were poured through a layer of mesh into a beaker. All cells weretransferred to one 225 ml-centrifuge tube and centrifuged down at 20°C., 470×g for 7 minutes in a bench top centrifuge. After discarding thesupernatant, the pellet was resuspended in 1 ml fresh pre-warmed (37°C.) serum free growth medium comprising 10 ng/ml EGF per trunk bypipetting up and down thoroughly. Fresh prewarmed (37° C.) serum freegrowth medium comprising 10 ng/ml EGF was added to a total volume of 150ml. The centrifugation step was repeated. The supernatant was removedand the pellet was resuspended as described above. Fresh prewarmed (37°C.) serum free growth medium comprising 10 ng/ml EGF was added to atotal volume of 100 ml. Cells were counted as described in the followingsection. The required amounts of cells were seeded in roller bottleswith serum free growth medium comprising 10 ng/ml EGF and incubated at37° C. Cells were ready for virus infection at day four after seeding.

EXAMPLE 2 Counting Cell Density

A sample of the cell suspension (see section CEF preparation) was takenand mixed with one volume of Trypan blue, resulting in a final cellcount of 20 to 100 cells per 16 small squares of a hemocytometersupplied by Fuchs-Rosenthal under the name of Hemocytometer Fast Read102 (1:2-1:10 dilution). The sample was taken immediately afterresuspending the cells in order to prevent reaggregation orsedimentation of the cells. After a few minutes of incubation time withTrypan blue in order to get the dye properly into dead cells, 10 μl ofthe cell suspension was added to the hemocytometer. Only white, livingcells were counted under a light microscope using a 10× objective. Intotal, 3 representative big squares consisting of 3×16 small ones werecounted. From every big square only two borders in L-Form were includedin the counting. The average of counted cells was taken and the finalcell concentration was calculated using the following formula: Averagecell number×dilution×10⁴=cells/ml. Finally the cell suspension wasdiluted to the desired working concentration.

EXAMPLE 3 Effect of the Addition of a Factor Selected from GrowthFactors and Fibronectin to a Serum Free Culture Medium on the Formationof a CEF-monolayer

In preliminary experiments it was shown that CEF cells do not attach tothe surface of cell culture vessels if medium 199 is used that does notcomprise FCS. Moreover, no monolayers are formed. Normal monolayerformation is observed if medium 199 containing 7% FCS is used. It wasanalyzed whether attachment and growth of CEF cells in serum free medium199 can be achieved if recombinant Epidermal Growth Factor (rh-EGF) andFibronectin (FN) are added to the medium.

For the experiments CEF cells were grown in medium 199 with thedifferent additives alone or in combination. Cells grown in medium 199without any additives served as negative control. Cells cultivated inmedium 199 comprising 7% FCS served as positive control. All experimentswere conducted in 6-well cell culture plates with 3 ml medium. Theadditives were treated according to the data sheets of the supplierbefore being used for the cell culture. Fibronectin was allowed toadsorb to the surface of the cell culture plates for 25 minutes beforeuse. Fibronectin was used in a concentration of 3 μg/cm² and EGF wasused in a concentration of 10 ng/ml. Before adding any cells the cellculture plates were brought into contact with the fibronectin-containingmedium for 25 minutes.

Every culture medium plus the additives to be tested was cultured induplicate. The 6-well cell culture plates were incubated for 4 days at37° C. From day 1 to 4 the attachment and growth of the cells wasevaluated using a microscope.

For the positive control a normal attachment and growth of the CEF cellshas been observed. For Medium 199 without additives nearly no attachmentof CEF cells could be observed.

A crucial improvement in the forming of a monolayer was seen by the useof EGF added to Medium 199 compared to Medium 199 without additives. Itwas found that the cells attached and formed the typical fibroblastmorphology. Furthermore, a continuous growth could be observed over thewhole period of 4 days.

An improvement of cell attachment was also achieved by addingfibronectin to the culture medium. The addition of both, EGF andFibronectin resulted in a slight improvement compared to the addition ofEGF only and Fibronectin only.

In summary, monolayer formation of CEF cells in the serum-free Medium199 can be supported by the use of the additives EGF and Fibronectin.

Moreover, in parallel sets of experiments 1×10⁷ CEF cells were seeded inmedium comprising 10% FCS, medium not comprising FCS and medium notcomprising FCS but comprising EGF. The cell number was counted 2 daysafter seeding. The number of cells amounted to 42%, 6% and 44%,respectively, of the cell number used for seeding. Thus, the results forthe cells seeded in serum free medium comprising EGF were as good as theresults obtained with medium comprising FCS and significantly betterthan with medium neither containing serum nor EGF.

In addition the medium comprising EGF was compared to various standardserum free media, such as DMEM, Opti-Mem or 293-SFM. To this end 1×10⁷CEF cells were seeded in the various serum-free media and cultivated for4 days. The number of cells cultivated in medium comprising EGF was 24,5 and 12 times higher than the number of cells cultivated in serum freeDMEM, Opti.Mem and 293-SFM, respectively.

EXAMPLE 4 Infection of CEF Cells with MVA

CEF cells were infected four days after seeding in roller bottles. Atthat time point cells have grown to an adequate monolayer. Cells wereinfected with a MOI of 1 or 0.1 MVA. For the infection the growth mediumwas removed from the flasks. The desired amount of virus per rollerbottle was diluted in 20 ml of the appropriate infection medium withoutserum. At this stage the serum free medium may or may not comprise afactor selected from growth factors and fibronectin. Cells wereincubated with the virus for 1 hour at 37° C. at 0.3-0.5 rpm in a rollerbottle incubator. After 1 hour the roller bottles were filled with theappropriate serum free growth medium to a total volume of 200 ml perroller bottle. At this stage the serum free medium may or may notcomprise a factor selected from growth factors and fibronectin. Virusreplication was stopped after 48 or 72 hours by freezing the rollerbottles to −20° C.

EXAMPLE 5 Preparation of Viral Extracts from Infected CEF Cells andTitration of MVA

The frozen roller bottles were thawed at room temperature. During thethawing process the cells detach from the surface of the roller bottlesand can mechanically be removed by shaking the flasks. Virus/cellsuspension was harvested and aliquoted to smaller volumes. To releasethe virus from the infected cells, virus/cell suspensions were 3 timesfreeze/thawed. The freeze/thawed virus samples were used for titration.

Titrations were performed on 1^(st) passage CEF cells in 96-well plates,using 10-fold dilutions of viral suspension and 8 replicates perdilution. After the infection, infected cells were visualized with ananti-vaccinia virus antibody and an appropriate staining solution.

In detail, at day zero of the assay primary CEF cells (see section“preparation of Chicken Embryo Fibroblast (CEF) cells”) were trypsinizedand counted as described in the section “counting cell density”. Thecells were diluted to 1×10⁵ cells/ml in RPMI medium with 7% FCS.Following this dilution, 100 μl were seeded in each well of the 96-wellplates using a multichannel pipette. Cells were incubated over night at37° C. and 5% CO₂. The virus samples to be titrated (see section“preparation of viral extracts from infected CEF cells”) were seriallydiluted in 10-fold steps from 10⁻¹-10⁻¹² using RPMI without serum. Thisserial dilution is carried out by adding 900 μl RPMI to all the wells ofa 96-deep-well plate. 100 μl of virus sample was added to all the wellsof the first row and mixed. Thereafter, 100 μl of each sample weretransferred to the next row of wells using a multi-channel pipette. The96-deep-well plates were kept on ice when performing the dilutions.Plates were incubated for 5 days at 37° C. and 5%CO₂ to allow theinfection to proceed. After 5 days, cells were immunohistochemicallystained with a vaccinia virus specific antibody. For the staining, theculture medium was removed by turning the 96-well plate upside down overa receptacle. Cells were fixed with 100 μl/well methanol/acetone (1:1)mixture for 10 minutes at room temperature. The fixing solution wasremoved and plates were air-dried. After drying, cells were washed oncewith PBS and incubated for 1 hour at room temperature with theanti-vaccinia virus antibody (Anti-Vaccinia virus antibody, rabbitpolyclonal, IgG fraction (Quartett, Berlin, Germany #9503-2057) dilutedto 1:1000 in PBS with 3% FCS. After removing the antibody, cells werewashed twice with PBS and incubated for 1 hour at room temperature withHRP-coupled (Horseradish Peroxidase-coupled) anti-rabbit antibody(Anti-rabbit IgG antibody, HRP-coupled goat polyclonal (Promega,Mannheim, Germany # W4011) diluted to 1:1000 in PBS with 3% FCS. Again,cells were washed with PBS and stained either with o-Dianisidine or TMB.For using the o-Dianisidine staining method, cells were incubated with100 μl/well staining solution consisting of 5 mg o-Dianisidine and 180μl 30% H₂O₂ per 60 ml of 50 mM phosphate-citrate buffer. Cells wereincubated at room temperature until they stained brown. Infected cellswere clearly visible after 1-3 hours. Using the TMB staining method,cells were incubated with 30 μl/well 1.2 mM TMB (Seramun DiagnosticaGmbH). After 15 minutes incubation time, the TMB solution was removedand cells were washed once with PBS. Infected cells appear dark blue.The plates were scored for infected cells. The viral titer wascalculated using the formula of Spearman and Kaerber. For thecalculation of the TCID₅₀ every well showing brown or blue cells wasmarked positive. Because assay parameters are kept constant, thefollowing simplified formula was used:

^(i.) Virus titer [TCID₅₀/ml]=10^([a+1.5+xa/8+xb/8+xc/8])

-   -   b. a=dilution factor of last column, in which all eight wells        are positive    -   c. x_(a)=number of positive wells in column a+1    -   d. x_(b)=number of positive wells in column a+2    -   e. x_(c)=number of positive wells in column a+3

EXAMPLE 6 Optimal Seeding Density for CEF Cells in Serum Free Medium andOptimal Amount of MVA for Infection of CEF Cells

An optimal seeding cell density of 7.5×10⁷ cells/850 cm² (surface of oneroller flask) was determined for serum-free CEF growth. Cells were ableto build a good monolayer without forming big clumps at day four afterseeding and could be infected at this time point.

Experiments were carried out to determine the best level of viralinoculation and length of the infection for the maximum production ofMVA from CEF cells cultured in a serum-free process. CEF cells wereseeded at a density of 7.5×10⁷ cells/850 cm² in medium according to thepresent invention. At day 4 after seeding, cells were infected withdifferent amounts of MVA in the range of 0.05 to 1.0 TCID₅₀/cell of MVA.Best results were obtained with 0.1 TCID₅₀/cell of MVA.

EXAMPLE 7 Optimal pH of Serum Free Medium for Culturing and Infectionwith MVA

MVA and other poxvirus infections are sensitive pH below 7.0. Poxvirusesare not stable at acid pH and it is recommended that purified poxvirusesare stored in a buffered solution above pH 7.0 to ensure stability andviral integrity upon storage as a liquid viral preparation. Experimentswere carried out to determine the effect on virus yield when carryingout infection at different starting pH. Roller bottles were seeded withCEF cells in the usually way in serum free medium comprising 10 ng/mlEGF plus 4 mM L-glutamine and cultured for 4 days. Cells were infectedwith MVA at 0.1 TCID₅₀/cell in serum free medium comprising 10 ng/ml EGFplus L-glutamine and 1 mM asparagine at different pH's ranging from 6.5to 9.0. At 72 hours post infection, the pH of the medium was measuredand viral yields were determined by titrating cell extracts in the usualmanner. The results are presented in the following table, which showsthe effect of initial pH of the medium at the start of the infection onvirus yield.

serum free medium comprising 10 ng/ml EGF Starting pH pH at 72 h p.i.Titer [TCID₅₀/ml] 6.5 7.05 0.56 × 10⁷ 7.0 7.34 10.0 × 10⁷ 7.5 7.53 5.60× 10⁷ 8.0 7.68 8.60 × 10⁷ 8.5 7.75 7.80 × 10⁷ 9.0 8.03 0.65 × 10⁷

For the infections carried out in serum free medium comprising 10 ng/mlEGF supplemented with L-glutamine and asparagine, the viral productionwas relatively constant with a starting pH from 7.0 to 8.5 but viralproductions were low at starting pH of 6.5 and 9.0. Best yield wasobtained at starting pH 7.0. Commercially available standard serum freemedia usually have a pH of 7.4. Therefore adjusting the pH of the serumfree medium to 7.0 can help to improve virus yield.

EXAMPLE 8 Effect of Added Asparagine to the Serum Free Medium

Preliminary experiments have revealed that the amount of asparagine maybe limiting during the cultivation of CEF cells and the infection of CEFcells with MVA. To overcome the depletion of asparagine in the serumfree media during the culturing and infection process, extra asparaginewas added to the medium as a supplement before infecting CEF cells. Todetermine the optimal amount of asparagine to supplement the mediumwith, roller bottles were seeded with CEF cells (7.5×10⁷ cells/850 cm²)in serum free medium comprising 10 ng/ml EGF plus 4 mM L-glutamine. Fourdays after seeding cells were infected with MVA at 0.1 TCID₅₀/cell inserum free medium comprising 10 ng/ml EGF plus 4 mM L-glutaminesupplemented with different asparagine concentrations (0.5, 1.0 and 1.5mM). Viral replication was stopped at 72 hours post infection and viraltiters were determined. The results are shown in the following tablethat shows the production of MVA from CEF cells supplemented withdifferent levels of asparagine for the infection stage. The titersrepresent the averages of 3 roller bottles per asparaginesupplementation.

Supplement Viral titers after 72 hours infection Asparagine [TCID₅₀/ml]0.0 mM 1.8 × 10⁸ 0.5 mM 1.3 × 10⁸ 1.0 mM 6.8 × 10⁸ 1.5 mM 1.0 × 10⁸

The results demonstrate that supplementing the serum free mediumcomprising 10 ng/ml EGF medium with asparagine could improve viralproduction and that supplementation to 1 mM for the infection processwas optimal.

EXAMPLE 9 Re-derivation of Viruses

It is the aim of this example to show the usefulness of the methodsaccording to the present invention for the re-derivation of viruses. Wetherefore intentionally cultivate MVA-BN under standard serum containingconditions. Accordingly, such vaccine may potentially comprise undesiredviral contaminants or infectious agents such as BSE. The virus obtainedafter cultivation under serum containing conditions is then used asstarting material for the re-derivation of the virus under serum freeconditions according to methods described in the present application toobtain a re-derived virus stock wherein the risk of said virus tocontain a BSE particle is less than 10³².

MVA-BN virus seed stock: The starting material for a re-derived MVA-BNvirus seed stock is an inoculate obtained by intentionally cultivatingMVA-BN under standard serum containing conditions (10% fetal calfserum).

Primary CEF Cells: Primary CEF cells are prepared from certified SPFeggs as outlined below. Certified fertilised SPF eggs are supplied byCharles River SPAFAS. The flocks at Charles River are tested accordingto European Pharmacopoeia section 5.2.2 (REF 12.4). Upon arrival thepackage and the eggs are checked visually for damage and dirt. Damagedeggs are removed. The eggs are stored refrigerated for not longer than12 days at +2° C. to 8° C. Before incubation the eggs are disinfected byspraying with Mel Sept and put into an egg incubator. Incubation isperformed for 10 to 12 days (preferable 11 days) at 37.8° C. +/−0.8° C.and 60% +/−10% relative humidity.

-   Prior to cell preparation the eggs are transferred to a dedicated    egg carton and extensively treated with Mel Sept by spraying. The    eggs are allowed to dry under a laminar flow.-   The eggs are opened and the embryos are removed. Dead embryos and    embryos showing deformations are excluded.-   The heads and feet of the embryos are cut off.-   Trunks are homogenised mechanically by squeezing them in a plastic    syringe.-   Cells are incubated at room temperature with Trypsin/EDTA solution    while stirring.-   Homogenised cells are poured through one layer of mesh and    collected.-   The homogenised cells are centrifuged. The supernatant is discarded    and the cell sediment is washed with a serum free medium according    to the present invention.-   The cells are pelleted again by centrifugation.-   The supernatant is discarded and the cells are re-suspended in a    serum free medium according to the present invention.-   Cells are counted and immediately seeded in a serum free medium in    appropriate culture vessels.

Plaque purification and final amplification of selected clone: The 5rounds of plaque purification by limited dilution are conducted.

Seeding of Cells:

-   Primary CEF cells are seeded in a T175 flask (1×10⁷ cells/flask) in    a serum free medium according to the present invention and incubated    at 37° C.+/−2° C. for 3 to 8 days.-   First passage CEF cells are seeded in 96 well plates (1-2×10⁵    cells/ml) using a serum free medium according to the present    invention and incubated for 24 h at 37° C. +/−2° C.-   Approximately 10 plates are used per round of plaque purification.

Infection of Cells:

-   10 fold serial virus dilutions (10⁻¹ to 10⁻¹⁰) are prepared in a    serum free medium according to the present invention. 100 μl of the    virus dilution/well are transferred to the 96 well plates containing    CEF cells.-   The plates are incubated for 5 to 6 days at 37° C.+/−2° C.

Isolation of Plaques:

-   Single virus plaques are visually detected under a microscope. 5 to    10 single plaques are collected per round of plaque purification.-   Each plaque is harvested using a pipette tip by scrapping and    transferred to a 1.5 ml tube. The volume is adjusted to 200 μl with    a serum free medium according to the present invention.-   The virus is released from the harvested cells by three cycles of    freeze-thawing: freeze tube in liquid Nitrogen or at −80° C., thaw    at room temperature, repeat procedure twice.-   The virus suspension can be stored at −80° C. until further    analysis. Alternatively if only one single virus plaque is detected    per well, cells can be harvested by freeze-thawing the whole 96 well    plate three-times.-   For amplification, 100 μl of the virus suspension is transferred to    cells grown in 12 well plates.

Amplification of Virus on 12 Well Plates:

-   First passage CEF cells are seeded in 12 well plates (5×10⁴    cells/cm²) in 1 ml of a serum free medium according to the present    invention and incubated for 24 h at 37° C.+/−2° C.-   Cells show 80 to 100% confluence for infection.-   100 μl of the virus suspension are added/well.-   Cells are incubated for 48 to 72 h.-   After 48 to 72 h the medium is removed and 300 μl of PBS per well    are added. Cells are harvested in PBS and transferred to a 1.5 ml    tube. If cells are already detached they are harvested (by scraping)    directly in the media and transferred to a 1.5 ml tube.-   The virus is released from the harvested cells by three cycles of    freeze-thawing: freeze tube in liquid Nitrogen or at −80° C., thaw    at room temperature, repeat procedure twice.-   The virus suspension can be stored at −80° C. until further    analysis.

Screening of Amplified Virus:

-   200 μl of the solution are used for DNA preparation and PCR    screening.-   The remaining 100 μl are used for the next plaque purification    round.

Final amplification of selected clone: After 5 rounds of plaquepurification, the final selected clone is further amplified to obtainenough material to produce a new master seed. The minimal amount ofvirus needed for production of a new master seed is 1×10⁸ TCID₅₀ in16-20 ml. The selected clone (already amplified on a 12 well plate) istransferred to a T25 cell culture flask for amplification. The cellvirus suspension is harvested by three cycles of freeze-thawing. Thevirus suspension is then transferred to a T75 cell culture flask foramplification and harvested. The virus is released by 3 cycles offreeze-thawing. Final amplification is performed in 3 to 5 T175 cellculture flasks. Material from 3 to 5 T175 flasks is harvested andsubjected to 3 cycles of freeze-thawing. The virus suspension istitrated, checked for sterility and tested for identity by PCR analysisof the 6 deletion sites.

Production of new master seed: Primary CEF cells are seeded in rollerbottles (850 cm²) with 7.5×10⁷ CEF cells in 200 ml of a serum freemedium according to the present invention. 2 to 5 roller bottles areseeded and incubated for 4 days at 37° C.+/−2° C., 0.3 rpm (±0.2 rpm) ina roller incubator. A virus suspension is prepared with a final titer of1.0×1×10⁶ TCID₅₀ (±0.5 log) in RPMI media. 10 ml are needed per rollerbottle. This corresponds to an MOI of 0.1. The medium is removed fromthe roller bottles. 10 ml of the virus suspension is added to eachroller bottle and incubated for 1-3 hrs in a roller incubator. 140 mlRPMI are added and incubated for 72 hours (±8 hours), 0.5 rpm (±0.2rpm).

Bottles are checked macroscopically for microbial contamination. Theroller bottles are transferred into a −20° C. freezer, and thecell/virus suspension is allowed to freeze. The roller bottles arestored at room temperature until the suspension has started to thaw andremove cells from the wall by shaking thoroughly. The cell/virussuspension is allowed to thaw completely. The cell/virus suspension isharvested into an appropriate vessel and aliquot a 4.5 ml in 5 mlcryotubes. Approximately 100 vials can be obtained from one rollerbottle. Filled virus suspension is stored at −20° C.

EXAMPLE 10 Growth Kinetics of a Strain of MVA Cultured in Serum FreeMedium in Selected Cell Lines and Replication In Vivo

Growth kinetics in cell lines: To characterize a newly isolated strainof the present invention (further referred to as MVA-BN) which iscultured in serum free media, the growth kinetics of the new strain arecompared to those of known MVA strains that have already beencharacterized.

The experiment compares the growth kinetics of the following viruses inthe subsequently listed primary cells and cell lines:

-   -   a. MVA-BN    -   b. MVA as characterized by Altenburger (U.S. Pat. No. 5,185,146)        and further referred to as MVA-HLR;    -   c. MVA (passage 575) as characterized by Anton Mayr (Mayr, A.,        et al. [1975] Infection 3; 6-14) and further referred to as        MVA-575 (ECACC V00120707); and    -   d. MVA (passage 572) and further referred to as MVA-572 (ECACC        V94012707); and    -   e. MVA-Vero as characterized in the International Patent        Application PCT/EP01/02703 (WO 01/68820); Virus stock, passage        49, #20, 22.03.99 crude, titered at 4.2×10⁷ TCID₅₀/ml.        The primary cells and cell lines used are:    -   a. CEF Chicken embryo fibroblasts (freshly prepared from SPF        eggs);    -   b. HeLa Human cervix adenocarcinoma (epithelial), ATCC No.        CCL-2;    -   c. 143B Human bone osteosarcoma TK-, ECACC No. 91112502;    -   d. HaCaT Human keratinocyte cell line, Boukamp et at. 1988, J        Cell Biol 106(3): 761-771;    -   e. BHK Baby hamster kidney, ECACC 85011433;    -   f. Vero African green monkey kidney fibroblasts, ECACC 85020299;    -   g. CV1 African green monkey kidney fibroblasts, ECACC 87032605.

For infection the cells are seeded onto 6-well-plates at a concentrationof 5×10⁵ cells/well and incubated overnight at 37° C., 5% CO₂ in DMEM(Gibco, Cat. No. 61965-026) with 2% FCS. The cell culture medium isremoved and cells are infected at approximately moi 0.05 for one hour at37° C., 5% CO₂ (for infection it is assumed that cell numbers doubledover night). The amount of virus used for each infection is 5×10⁴ TCID₅₀and is referred to as Input. The cells are then washed 3 times with DMEMand finally 1 ml DMEM, 2% FCS is added and the plates are left toincubate for 96 hours (4 days) at 37° C., 5% CO₂. The infections arestopped by freezing the plates at −80° C.; followed by titrationanalysis.

Titration Analysis (Immunostaining with a Vaccinia Virus SpecificAntibody):

For titration of amount of virus test cells (CEF) are seeded on96-well-plates in RPMI (Gibco, Cat. No. 61870-010), 7% FCS, 1%Antibiotic/Antimycotic (Gibco, Cat. No. 15240-062) at a concentration of1×10⁴ cells/well and incubated over night at 37° C., 5% CO₂. The6-well-plates containing the infection experiments are frozen/thawed 3times and dilutions of 10⁻¹ to 10⁻¹² are prepared using RPMI growthmedium. Virus dilutions are distributed onto test cells and incubatedfor five days at 37° C., 5% CO₂ to allow CPE (cytopathic effect)development. Test cells are fixed. (Acetone/Methanol 1:1) for 10 min,washed with PBS and incubated with polyclonal vaccinia virus specificantibody (Quartett Berlin, Cat. No. 9503-2057) at a 1:1000 dilution inincubation buffer for one hour at RT. After washing twice with PBS(Gibco, Cat. No. 20012-019) the HRP-coupled anti-rabbit antibody(Promega Mannheim, Cat. No. W4011) is added at a 1:1000 dilution inincubation buffer (PBS containing 3% FCS) for one hour at RT. Cells areagain washed twice with PBS and incubated with staining solution (10 mlPBS+200 μl saturated solution of o-dianisidine in 100% ethanol+15 μlH₂O₂ freshly prepared) until brown spots are visible (two hours).Staining solution is removed and PBS is added to stop the stainingreaction. Every well exhibiting a brown spot is marked as positive forCPE and the titer is calculated using the formula of Kaerber (TCID₅₀based assay) (Kaerber, G. 1931. Arch. Exp. Pathol. Pharmakol. 162, 480).

Cell preparations are infected with investigational viruses as definedabove with the exception that MVA-BN is cultured in serum free media andthe other investigational viruses are not cultured in serum free mediaand incubated for 96 hours. The infections are stopped by freezing at−80° C., followed by titration analysis as described above.

Investigational viruses amplify well in CEF cells. In Vero and CV1cells, MVA-BN is distinguished for not amplifying well in these cells.In human cells 143B, HeLa and HaCaT, MVA-BN is distinguished for beingthe only investigational virus to demonstrate complete attenuation,exhibiting a significant decrease over input. Consequently, it isdemonstrated that MVA-BN cultivated in a serum free environment exhibitscritical attenuation over other known MVA cultivated in a variety ofanimal and human cell lines.

The viruses are used to infect duplicate sets of cells that are expectedto be permissive for MVA (i.e., CEF and BHK) and cells expected to benon-permissive for MVA (i.e., CV-1, Vero, Hela, 143B and HaCaT). Thecells are infected at a low multiplicity of infection, i.e., 0.05infectious units per cell (5×10⁴ TCID₅₀). The virus inoculum is removedand the cells are washed three times to remove any remaining unadsorbedviruses. Infections are left for a total of 4 days when viral extractsare prepared and then titered on CEF cells.

It is demonstrated that all viruses amplified well in CEF cells asexpected, since this is a permissive cell line for all MVAs.Additionally, it is demonstrated that all viruses amplified well in BHK(Hamster kidney cell line). MVA-Vero performs the best, since BHK is apermissive cell line for this strain.

Concerning replication in Vero cells (Monkey kidney cell line), MVA-Veroamplifies well, as expected. MVA-HLR, MVA-575 and MVA-572 amplify wellwith a significant increase above Input. Only MVA-BN is found to notamplify as well in these cells when compared to the other strains.

Also concerning replication in CV1 cells (Monkey kidney cell line) it isfound that MVA-BN is highly attenuated in this cell line. It exhibits a200-fold decrease below Input. MVA-575 does not amplify above the Inputlevel and also exhibits a slight negative amplification. MVA-HLRamplifies the best with a significant increase above Input, followed byMVA-Vero and MVA-572.

It is most interesting to compare the growth kinetics of the variousviruses in human cell lines. Regarding reproductive replication in 143Bcells (human bone cancer cell line) it is demonstrated that MVA-Vero isthe only strain to show amplification above Input. All other viruses donot amplify above Input, however there is a big difference between theMVA-HLR and MVA-BN, MVA-575 and MVA-572. MVA-HLR is “borderline”,whereas MVA-BN exhibits the greatest attenuation, followed by MVA-575and MVA-572. To summarize, MVA-BN is superior with respect toattenuation in human 143B cells.

Furthermore, concerning replication in HeLa cells (human cervix cancercells) it is demonstrated that MVA-HLR amplifies well in this cell line,and even better than it did in the permissive BHK cells. MVA-Vero alsoamplified in this cell line. However, MVA-BN, and also to a lesserextent MVA-575 and MVA-572, are attenuated in these cell lines.

Concerning the replication in HaCaT cells (human keratinocyte cellline), it is demonstrated that MVA-HLR amplifies well in this cell line.MVA-Vero adapted and MVA-575 and MVA-572 exhibit amplification in thiscell line. However, MVA-BN is the only one to demonstrate attenuation).

From this experimental analysis, we may conclude that MVA-BN is the mostattenuated strain in this group of viruses. MVA-BN demonstrates extremeattenuation in human cell lines. Thus, MVA-BN is the only MVA strainexhibiting an amplification ratio of less than 1 in each human cell lineexamined, i.e., 143B, Hela, HaCaT, and 293.

MVA-575 exhibits a profile similar to that of MVA-BN, however it is notas attenuated as MVA-BN.

MVA-572 is less attenuated than MVA-575.

MVA-HLR amplifies well in all (human or otherwise) cell lines tested,except for 143B cells. Thus, it is regarded as replication competent inall cell lines tested, with the exception of 143B cells. In one case, iteven amplifies better in a human cell line (HeLa) than in a permissivecell line (BHK).

MVA-Vero does exhibit amplification in all cell lines, but to a lesserextent than demonstrated by MVA-HLR (ignoring the 143B result).Nevertheless, it cannot be considered as being in the same “class” withregards to attenuation, as MVA-BN or MVA-575.

EXAMPLE 11 Replication In Vivo

Given that some MVA strains clearly replicate in vitro, different MVAstrains are examined with regard to their ability to replicate in vivousing a transgenic mouse model AGR129. This mouse strain has targetedgene disruptions in the IFN receptor type I (IFN-α/β) and type II(IFN-γ) genes, and in RAG. Due to these disruptions, the mice have noIFN system and are incapable of producing mature B and T cells and, assuch, are severely immune-compromised and highly susceptible to areplicating virus. Groups of six mice are immunized (i.p) with 10⁷ pfuof either MVA-BN, which is cultured in serum free media, MVA-HLR,MVA-572 (used in 120,000 people in Germany) or MVA-575 and monitoreddaily for clinical signs. All mice vaccinated with MVA-HLR or MVA-572die within several weeks. At necropsy, there are general signs of severeviral infection in the majority of organs. A standard plaque assaymeasures the recovery of MVA (10⁸ pfu) from the ovaries. In contrast,mice vaccinated with the same dose of MVA-BN (corresponding to thedeposited strain ECACC V00083008) survive for more than 90 days and noMVA-BN is recovered from organs or tissues.

When taken together, data from the in vitro and in vivo studies clearlydemonstrate that MVA-BN cultured in serum free media is more highlyattenuated than the parental and commercial MVA-HLR strain, as well asMVA-575 and MVA-572, and may be safe for administration toimmune-compromised subjects.

EXAMPLE 12 Immunological and In Vivo Data in Animal Model Systems

These experiments are designed to compare different dose and vaccinationregimens of MVA-BN compared to other MVAs in animal model systems.

Different Strains of MVA Differ in their Ability to Stimulate the ImmuneResponse:

Replication competent strains of vaccinia induce potent immune responsesin mice and at high doses are lethal. Although MVA are highly attenuatedand have a reduced ability to replicate on mammalian cells, there aredifferences in the attenuation between different strains of MVA. Indeed,MVA-BN appears to be more attenuated than other MVA strains, even theparental strain MVA-575. To determine whether this difference inattenuation affects the efficacy of MVA to induce protective immuneresponses, different doses of MVA-BN which is cultured in serum freemedium and MVA-575 or MVA-572 are compared in a lethal vacciniachallenge model. The levels of protection are measured by a reduction inovarian vaccinia titers determined 4 days post challenge, as this allowsa quantitative assessment of different doses and strains of MVA.

Lethal Challenge Model:

Specific pathogen-free 6-8-week-old female BALB/c (H-2d mice (n=5) areimmunized (i.p.) with different doses (10², 10⁴ or 10⁶ TCID₅₀/ml) ofeither MVA-BN which is cultured in serum free medium, MVA-575 orMVA-572. MVA-BN, MVA-575 and MVA-572 are propagated on CEF cells (MVA-BNbeing propagated in serum free media), and are sucrose purified andformulated in Tris pH 7.4. Three weeks later the mice receive a boost ofthe same dose and strain of MVA, which is followed two weeks later by alethal challenge (i.p.) with a replication competent strain of vaccinia.As replication competent vaccinia virus (abbreviated as “rVV”) eitherthe strain WR-L929 TK+ or the strain IHD-J are used. Control micereceive a placebo vaccine. The protection is measured by the reductionin ovarian titers determined 4 days post challenge by standard plaqueassay. For this, the mice are sacrificed on day 4 post the challenge andthe ovaries are removed, homogenized in PBS (1 ml) and viral titersdetermined by standard plaque assay using VERO cells (Thomson, et al.,1998, J. Immunol. 160: 1717).

Mice vaccinated with two immunizations of either 10⁴ or 10⁶ TCID₅₀/ml ofMVA-BN which is cultured in serum free medium, MVA-575 or MVA-572 arecompletely protected as judged by a 100% reduction in ovarian rVV titers4 days post challenge. The challenge virus is cleared. However,differences in the levels of protection afforded by MVA-BN, MVA-575 orMVA-572 are observed at lower doses. Mice receiving two immunizations of10² TCID₅₀/ml of MVA 575 or MVA-572 fail to be protected, as judged byhigh ovarian rVV titers. In contrast, mice vaccinated with the same doseof MVA-BN exhibit a significant reduction in ovarian rVV titers. Thecontrol mice receiving a placebo vaccine have a mean viral titer of5.11×10⁷ pfu (+/−3.59×10⁷).

All strains of MVA induce protective immune responses in mice against alethal rVV challenge. Although all strains of MVA are equally efficientat higher doses, differences in their efficacy are clearly evident atsub-optimal doses. MVA-BN which is cultured in serum free medium is morepotent than its parent strain MVA-575 or MVA-572 at inducing aprotective immune response against a lethal rVV challenge, which may berelated to the increased attenuation of MVA-BN compared to MVA-575 andMVA-572.

EXAMPLE 13 MVA-BN in Prime/Boost Vaccination Regimes

Induction of Antibodies to MVA Following Vaccination of Mice withDifferent Smallpox Vaccines

The efficacy of MVA-BN which is cultured in serum free medium iscompared to other MVA and vaccinia strains previously used in theeradication of smallpox. These include single immunizations using theElstree and Wyeth vaccinia strains produced in CEF cells and given viatail scarification, and immunizations using MVA-572 that was previouslyused in the smallpox eradication program in Germany or MVA-575. Inaddition, MVA-BN, MVA 572 and MVA-575 are compared as a pre-vaccinefollowed by Elstree via scarification. For each group eight BALB/c miceare used and all MVA vaccinations (1×10⁷ TCID₅₀) are given subcutaneousat week 0 and week 3. Two weeks following the boost immunization themice are challenged with vaccinia (IHD-J) and the titers in the ovariesare determined 4 days post challenge. All vaccines and regimes induce100% protection.

The immune responses induced using these different vaccines or regimesare measured in animals prior to challenge. Assays to measure levels ofneutralizing antibodies, T cell proliferation, cytokine production(IFN-γ vs IL-4) and IFN-γ production by T cells are used. The level ofthe T cell responses induced by MVA-BN, as measured by ELISPOT, isgenerally equivalent to other MVA and vaccinia viruses demonstratingbio-equivalence. A weekly analysis of the antibody titers to MVAfollowing the different vaccination regimes reveal that vaccinationswith MVA-BN significantly enhances the speed and magnitude of theantibody response compared to the other vaccination regimes. Indeed, theantibody titers to MVA are significantly higher (p>0.05) at weeks 2, 4and 5 (1 week post boost at week 4) when vaccinated with MVA-BN which iscultured in serum free medium compared to mice vaccinated with MVA-572or MVA-575. Following the boost vaccination at week 4, the antibodytiters are also significantly higher in the MVA-BN group compared to themice receiving a single vaccination of either the vaccinia strainsElstree or Wyeth. These results clearly demonstrate that 2 vaccinationswith MVA-BN induce a superior antibody response compared to theclassical single vaccination with traditional vaccinia strains (Elstreeand Wyeth) and confirm the findings that MVA-BN induces a higherspecific immunity than other MVA strains.

MVA-prime and boost regimes generate the same level of protection asDNA-prime/MVA-boost regimes in an influenza challenge model.

The efficacy of MVA prime/boost regimes to generate high avidity CTLresponses is assessed and is compared to DNA prime/MVA boost regimesthat have been reported to be superior. The different regimes areassessed using a murine polytope construct encoded by either a DNAvector or MVA-BN and the levels of CTL induction were compared byELISPOT; whereas the avidity of the response is measured as the degreeof protection afforded following a challenge with influenza.

Constructs

The DNA plasmid encoding the murine polytope (10 CTL epitopes includinginfluenza, ovalbumin) was described previously (Thomson, et al., 1998,J. Immunol. 160: 1717). This murine polytope is inserted into deletionsite II of MVA-BN, which is propagated on CEF cells in serum freemedium, sucrose purified and formulated in Tris pH 7.4.

Vaccination Protocols

In the current study, specific pathogen free 6-8 week old female BALB/c(H-2d) mice are used. Groups of 5 mice are used for ELISPOT analysis,whereas 6 mice per group are used for the influenza challengeexperiments. Mice are vaccinated with different prime/boost regimesusing MVA which is cultured in serum free medium or DNA encoding themurine polytope, as detailed in the results. For immunizations with DNA,mice are given a single injection of 50 μg of endotoxin-free plasmid DNA(in 50 μl of PBS) in the quadricep muscle. Primary immunizations usingMVA are done either by intravenous administration of 10⁷ pfu MVA-BN permouse, or by subcutaneous administration of 10⁷ pfu or 10⁸ pfu MVA-BNper mouse. Boost immunizations are given three weeks post primaryimmunization. Boosting with plasmid DNA is done in the same way as theprimary immunization with DNA (see above). In order to establish CTLresponses, standard ELISPOT assays (Schneider et al., 1998, Nat. Med. 4;397-402) are performed on splenocytes 2 weeks after the last boosterimmunization using the influenza CTL epitope peptide (TYQ), the P.Berghei epitope peptide (SYI), the Cytomegalovirus peptide epitope (YPH)and/or the LCV peptide epitope (RPQ).

For the challenge experiments, mice are infected i.n. with a sub-lethaldose of influenza virus, Mem71 (4.5×10⁵ pfu in 50 ml PBS). At day 5post-infection, the lungs are removed and viral titers are determined induplicate on Madin-Darby canine kidney cell line using a standardinfluenza plaque assay.

Efficacy of a MVA-BN nef Vaccine in SIV Infected Rhesus Monkeys.

To determine the efficacy of a MVA-BN nef vaccine, the viral load anddelay of disease following, a challenge with a virulent primary isolateof SIV are assessed. Another objective of the study is to determinewhether MVA-BN could be used to safely boost immune responses inimmune-compromised monkeys with a pre-existing immunity to MVA.

Vaccination Protocols

Two groups (n=6) of rhesus monkeys (Macaca mulatta) are vaccinated witha bolus intramuscular injection at week 0, 8 and 16, using either MVA-BNalone which is cultured in serum free medium or a recombinant MVA-BN nefwhich is cultured in serum free medium. On week 22, all monkeys arechallenged with 50 MID₅₀ of a pathogenic cell-associated SIV stock (1XC)from primary, uncultured rhesus monkey PBMC by the intravenous route.The clinical status of the animals is frequently monitored and regularblood samples are taken for the measurement of viremia, immuneparameters, and a full range of hematology and blood clinical chemistryparameters. Animals that develop AIDs-like disease are sacrificed. Thesurviving monkeys are monitored for 99 weeks post vaccination. At week100 the surviving monkeys are immunized i.m. with MVA-BN tat which iscultured in serum free medium and receive further immunizations with thesame MVA-BN tat at week 102 and 106.

This study demonstrates that MVA-BN which is cultured in serum freemedia is able to prime/boost immune responses in immune-compromisedrhesus monkeys. It also demonstrates that MVA-BN immunizations are safeand do not affect the levels of viremia in SIV infected animals. Thedelay in the progression of AIDS-like disease in the animals vaccinatedwith the MVA-BN nef, which is cultured in serum free medium, indicatesthat an immune response is successfully generated to nef.

Therapeutic Vaccination of SIV-Infected Monkeys UndergoingAnti-Retroviral Treatment

An MVA-BN based therapeutic HIV vaccine is likely to be used inindividuals undergoing anti-retroviral therapy. Therefore, this study isdesigned to investigate the safety (effect on SIV levels) and efficacyof recombinant MVAs encoding a variety of SIV antigens (gag, pol, env,rev, tat, and nef) in SIV infected monkeys treated with PMPA. PMPA is anucleoside analogue that is effective against HIV and SIV (Rosenwirth,B. et al., 2000, J Virol 74,1704-11).

Constructs

All the recombinant MVA constructs are propagated on CEF cells in serumfree media, sucrose purified and formulated in Tris pH 7.4.

Vaccination Protocol

Three groups (n=6) of rhesus monkeys (Macaca mulatta) are infected with50 MID₅₀ of a pathogenic primary Sly isolated (1XC) and then treateddaily with PMPA (60 mg/kg given s.c.) for 19 weeks. At week 10, animalsare vaccinated with recombinant MVA-BN (i.m.), or saline, and receiveidentical vaccinations 6 weeks later. Group 1 receives a mixture of MVAgag-pol and MVA-env, group 2 receives MVA-tat, MVA-rev and MVA-nef,whereas Group 3 receives saline. The clinical status of the animals isfrequently monitored and regular blood samples are taken for themeasurement of viremia, immune parameters, and a full range ofhematology and blood clinical chemistry parameters.

The present invention is not to be limited in scope by the specificembodiments described herein. Indeed, various modifications of theinvention in addition to those described herein will become apparent tothose skilled in the art from the foregoing description.

All patents, applications, publications, test methods, literature, andother materials cited herein are hereby incorporated by reference.

1-68. (canceled)
 69. An infected cell culture comprising chicken embryofibroblast cells (CEFs), wherein the CEFS have not previously beencultured in a medium containing serum, in a serum free medium, whereinthe CEFs are capable of replication for at least 4 days in the serumfree medium, wherein the CEFs are infected with a poxvirus, and whereinthe serum free medium comprises epidermal growth factor at aconcentration of 1-50 ng/ml.
 70. The cell culture of claim 69, whereinthe epidermal growth factor is human epidermal growth factor.
 71. Thecell culture of claim 70, wherein the epidermal growth factor isrecombinant human epidermal growth factor at a concentration of 5-50ng/ml.
 72. The cell culture of claim 71, wherein the epidermal growthfactor is recombinant human epidermal growth factor at a concentrationof 5-20 ng/ml.
 73. The cell culture of claim 69, wherein the serum freemedium comprises a fibronectin.
 74. The cell culture of claim 73,wherein the fibronectin is human plasma fibronectin.
 75. The cellculture of claim 74, wherein the fibronectin is human plasma fibronectinat a concentration of 1-10 μg/ml.
 76. The cell culture of claim 69,wherein the serum free medium comprises asparagine in the range of0.8-1.8 mM.
 77. The cell culture of claim 69, wherein the serum freemedium comprises glutamine in the range of 1-5 mM.
 78. The cell cultureof claim 69, wherein the poxvirus is a modified vaccinia Ankara (MVA)virus.
 79. A method for preparing a poxvirus preparation comprising:culturing the cell culture of claim 69; and isolating an poxviruspreparation from the infected cells.
 80. The method of claim 79, whereinthe preparation is free of products and infectious agents comprised inanimal serum.
 81. The method of claim 79, wherein the risk of thepreparation to contain a bovine spongiforme encephalopathy (BSE)particle is less than 10³².
 82. The method of claim 79, wherein thepoxvirus preparation comprises 10⁷ TCID₅₀of a modified vaccinia Ankara(MVA) virus.
 83. The method of claim 82, wherein the poxviruspreparation comprises 10⁸ TCID₅₀of a modified vaccinia Ankara (MVA)virus.
 84. A method for preparing a poxvirus preparation comprising:culturing the cell culture of claim 72; and isolating a poxviruspreparation from the infected cells.
 85. The method of claim 84, whereinsaid preparation is free of products and infectious agents comprised inanimal serum.
 86. The method of claim 84, wherein the risk of thepreparation to contain a bovine spongiforme encephalopathy (BSE)particle is less than 10³².
 87. The method of claim 84, wherein thepoxvirus preparation comprises 10⁷ TCID₅₀ of a modified vaccinia Ankara(MVA) virus.
 88. The method of claim 87, wherein the poxviruspreparation comprises 10⁸ TCID₅₀ of a modified vaccinia Ankara (MVA)virus.